Sodium ferric sulfate positive electrode sheet, dry preparation method thereof and sodium ion battery
By rapidly mixing carbon-coated sodium ferric sulfate particles with a conductive agent and performing fiberization, combined with rolling under low humidity conditions, the conductivity and strength issues of sodium ferric sulfate cathode materials were solved, achieving efficient and environmentally friendly dry electrode preparation and improving battery performance.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- CHAOWEI POWER GROUP CO LTD
- Filing Date
- 2026-01-15
- Publication Date
- 2026-05-29
AI Technical Summary
Existing technologies make it difficult to construct an efficient three-dimensional conductive network in sodium ferric sulfate cathode materials. Furthermore, in dry electrode processes, it is difficult for sodium ferric sulfate particles and PTFE binders to form a strong bond, resulting in poor electrode strength. In addition, traditional processes are time-consuming, energy-intensive, and environmentally unfriendly.
Carbon-coated sodium ferric sulfate particles are mixed with a positive electrode conductive agent at high speed to form a core-shell structure. After being mixed with a positive electrode binder, the mixture is subjected to high-speed shearing and fiberization treatment. Combined with rolling under low humidity conditions, a self-supporting positive electrode film is formed, ensuring conductivity and strength.
The conductivity and mechanical strength of the sodium ferric sulfate positive electrode were improved, water sensitivity issues were avoided, production costs were reduced, and electrochemical performance was improved.
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Figure CN122117816A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of sodium-ion battery cathode material technology, and particularly to a sodium iron sulfate cathode sheet, its dry preparation method, and a sodium-ion battery. Background Technology
[0002] Sodium-ion batteries have shown great application potential in the field of large-scale energy storage due to their abundant resources and low cost. Among the many cathode materials, sodium iron sulfate has attracted much attention due to its high voltage platform of 3.8 V, abundant iron and sulfur resources, excellent thermal stability and theoretical capacity. Hard carbon is currently the most mature and commercially promising anode material for sodium-ion batteries. However, sodium iron sulfate has two fatal drawbacks: (1) extremely poor intrinsic electronic conductivity; (2) very sensitive to moisture, easily undergoing hydration reaction, leading to structural failure. Traditional wet electrode process requires the use of organic solvents such as N-methylpyrrolidone to dissolve or disperse binders, active materials, etc., to make a slurry, and then coat it onto the current collector. This process has obvious defects for sodium iron sulfate: first, the slurry preparation and drying process is time-consuming and energy-intensive, costly and environmentally unfriendly; second, even with the use of organic solvents, it is difficult to completely avoid the material from contacting trace amounts of moisture, leading to material performance degradation; finally, sodium iron sulfate has poor affinity with commonly used binders, and wet coating easily leads to electrode cracking and powdering.
[0003] The dry electrode process requires no solvents; it directly dry-mixes the active material, conductive agent, and binder. The binder then forms a fiber network through fibrillation, bonding the components together. Finally, a self-supporting electrode film is formed through roll forming. This process perfectly avoids the water sensitivity issue of sodium ferric sulfate and offers advantages such as energy saving, environmental friendliness, and high production efficiency.
[0004] Currently, dry electrode technology is mostly used in lithium iron phosphate or ternary materials in the lithium battery field, and in combination with silicon-carbon anodes. However, applying the dry electrode process to the specific sodium battery system of sodium iron sulfate and hard carbon faces many challenges: 1. The extremely poor conductivity of sodium iron sulfate requires the construction of a more efficient three-dimensional conductive network in the dry electrode. 2. It is difficult for sodium iron sulfate particles to form a strong bond with the fiber network of dry binders such as PTFE, resulting in poor electrode strength. 3. The dry process is more sensitive to the particle size, morphology, and surface properties of the material, and general dry process parameters cannot be directly applied.
[0005] It is necessary to develop new dry electrode processes for sodium ferric sulfate / hard carbon systems to improve the conductivity, strength, and stability of the electrodes. Summary of the Invention
[0006] The purpose of this invention is to provide a dry electrode preparation method and sodium-ion battery that solves the water sensitivity problem of sodium ferric sulfate, thereby improving the adhesion and strength of the electrode and thus improving its conductivity and electrochemical performance.
[0007] The technical solution adopted in this invention is: A dry preparation method for sodium ferric sulfate positive electrode sheets, the method comprising: Carbon-coated sodium ferric sulfate particles are mixed with a positive electrode conductive agent at high speed, and the resulting composite is then mixed with a positive electrode binder. The composite is then subjected to high-speed shearing and fiberization to obtain a dry electrode mixture. The dry electrode mixture is then rolled and calendered to obtain a positive electrode film. The carbon-coated sodium ferric sulfate particles are made of D 50 Large particles of 5-10 μm and D 50 It consists of fine particles of 0.5-2 μm in a mass ratio of 7:3 to 9:1.
[0008] The carbon coating of the sodium ferric sulfate particles has a thickness of 2-20 nm. The carbon layer on the surface of the sodium ferric sulfate particles not only improves the intrinsic conductivity but also isolates air and moisture, providing a more stable raw material for the dry process.
[0009] The carbon source for coating is glucose, sucrose, pitch, or pyrolytic carbon from polyvinylidene fluoride.
[0010] The positive electrode conductive agent is at least one of Ketjen black, carbon nanotubes, and graphene.
[0011] In this invention, the positive electrode conductive agent and carbon-coated sodium ferric sulfate particles are pre-combined by high-speed mechanical mixing to form a "core-shell" structure, so that the conductive agent is coated on the surface of the sodium ferric sulfate particles.
[0012] Furthermore, the positive electrode binder is PTFE fine powder with a particle size of 100-500 μm.
[0013] Furthermore, based on the aforementioned carbon-coated sodium ferric sulfate particles, positive electrode conductive agent, and positive electrode binder, the mass percentage of each component is as follows: carbon-coated sodium ferric sulfate particles 85-93%, positive electrode conductive agent 3-8%, and positive electrode binder 4-7%.
[0014] Furthermore, the carbon-coated sodium ferric sulfate particles are mixed with the positive electrode conductive agent at high speed, typically in a high-speed mixer at a speed of 2000-5000 rpm for 5-15 minutes. After high-speed mixing, the positive electrode conductive agent is uniformly adhered to the surface of the carbon-coated sodium ferric sulfate particles.
[0015] The resulting composite is then mixed with a positive electrode binder and subjected to high-speed shear fiberization treatment. This is typically carried out in a high-speed shear mixer at a speed of 1000-3000 rpm for 3-10 minutes.
[0016] The rolling calendering is generally performed using a twin-roll press at room temperature to form a self-supporting positive electrode film.
[0017] During rolling, the calendering gap and pressure are controlled to ensure that the porosity of the final positive electrode film is 20%-40%; the rolling speed ratio is 1:1.2~1:1.5, and the rolling line pressure is 2-10 kN / cm.
[0018] Furthermore, the method of the present invention is carried out in an environment with a relative humidity of <10%.
[0019] The present invention also provides a sodium ferric sulfate positive electrode sheet prepared by the above method. The thickness of the positive electrode sheet is 160-200 μm.
[0020] The present invention also provides the application of the sodium ferric sulfate positive electrode sheet in the preparation of sodium-ion batteries.
[0021] The present invention also provides a sodium-ion battery, including the sodium iron sulfate positive electrode.
[0022] Furthermore, the sodium-ion battery includes a positive electrode and a negative electrode, which are prepared by the following method: (1) Carbon-coated sodium ferric sulfate particles are mixed with positive electrode conductive agent at high speed, and the resulting composite is then mixed with positive electrode binder and subjected to high-speed shearing fiberization treatment to obtain dry electrode mixture; the dry electrode mixture is rolled and calendered to obtain positive electrode film. (2) Hard carbon, negative electrode conductive agent and negative electrode binder are mixed and fiberized under high speed shearing. The resulting negative electrode mixture is rolled and calendered to obtain a negative electrode film. (3) The obtained positive electrode film and negative electrode film are hot-pressed or laminated onto the corresponding metal current collector by a small amount of adhesive to obtain the dry positive electrode and the dry negative electrode respectively.
[0023] The specific surface area of the hard carbon is 2-10 m². 2 / g,D 50 The particle size is 5-15 μm.
[0024] The negative electrode conductive agent is at least one of acetylene black, Super P, and Ketjen black.
[0025] The negative electrode binder is PTFE fine powder with a particle size of 100-500 μm.
[0026] Based on the aforementioned hard carbon, negative electrode conductive agent, and negative electrode binder, the mass percentages of each component are as follows: hard carbon 85-94%, negative electrode conductive agent 3-8%, and negative electrode binder 3-7%.
[0027] In step (2), the high-speed shearing fiberization process is generally carried out in a high-speed shear mixer with a rotation speed of 800-2500 rpm and a fiberization time of 3-8 minutes.
[0028] The rolling calendering is generally performed using a twin-roll press at room temperature to form a self-supporting negative electrode film.
[0029] Furthermore, the high-speed shearing fiberization process is carried out at a temperature controlled between 15-30°C and in a dry atmosphere with a relative humidity of <10%.
[0030] Furthermore, the sodium-ion battery includes a positive electrode, a negative electrode, a separator, and an electrolyte.
[0031] The sodium-ion battery can be used in large-scale energy storage systems, low-speed electric vehicles, or as a backup power source.
[0032] This invention provides a dedicated dry electrode process for sodium ferric sulfate / hard carbon systems. The entirely dry process completely avoids contact between sodium ferric sulfate and any solvent, ensuring the chemical stability of the material from the outset. During cathode preparation, pre-composite and particle size distribution are employed. A conductive agent is pre-composite, followed by a fibrous binder, ensuring controllable fibrosis. The entire process is conducted in a low-humidity environment (<10%RH), resulting in a cathode sheet with low resistance, high strength, and no powder shedding. It possesses high electronic / ionic conductivity, high mechanical strength, and excellent interfacial properties, exhibiting significantly superior electrochemical performance (capacity, rate capability, and cycle life) compared to sodium ferric sulfate electrodes prepared using traditional wet processes. Furthermore, the dry process eliminates the need for solvents, coating, and drying, saving expensive and energy-intensive equipment and processes, greatly reducing production costs, and is more environmentally friendly. This is of great significance for promoting the development of low-cost, high-performance sodium-ion batteries. Attached Figure Description
[0033] Figure 1 The positive and negative electrodes prepared for Example 1, Comparative Example 1, and Comparative Example 2 were used to prepare batteries, and charge-discharge tests were conducted at a rate of 0.5 C. The comparison chart shows the specific capacity of the first discharge. Detailed Implementation
[0034] The technical solution of the present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.
[0035] Example 1
[0036] I. Raw material preparation: The positive electrode active material, conductive agent, and binder are respectively: carbon-coated sodium ferric sulfate (large particles with D50=8 μm and fine particles with D50=1 μm are mixed at a mass ratio of 9:1), Ketjen black, and PTFE fine powder (particle size of 200 μm).
[0037] The negative electrode active material, conductive agent, and binder are respectively: hard carbon (D50=10 μm), Super P, and PTFE fine powder.
[0038] Carbon-coated sodium ferric sulfate can be prepared by the following method: Na₂SO₄ (355g), FeSO₄·H₂O (595g), and glucose (50g) were mixed and then coarsely and finely ground using sand mills of different specifications to obtain large-particle and small-particle precursors, respectively. After spray drying at 140℃, the mixture was heated to 370℃ at a rate of 5℃ / min and held for 12 hours under an argon atmosphere. After natural cooling, the mixture was removed and screened to obtain large-particle sodium ferric sulfate with a D50 of 8 μm and small-particle sodium ferric sulfate with a D50 of 1 μm, respectively. The carbon coating thickness was 12-20 nm.
[0039] Alternatively, commercially available carbon-coated sodium ferric sulfate can be purchased directly, and powders of different particle sizes can be sieved and particle size distribution can be carried out.
[0040] II. Cathode Preparation: a) Pre-composite: 900 g of graded carbon-coated sodium ferric sulfate and 50 g of Ketjen black were added to a high-speed mixer and dry-mixed at 3000 rpm for 10 minutes to obtain the composite.
[0041] b) Fiberization: The above composite and 50 g of PTFE powder were added to a high-speed shear mixer. The mixture was first mixed at 500 rpm for 1 minute, and then increased to 2000 rpm for 5 minutes to complete the fiberization.
[0042] c) Calendering: The mixed dry powder is fed into a two-roll press (roll temperature 25℃), with the roll gap set to 0.2 mm, the roll speed ratio to 1:1.3, and the linear pressure to 5 kN / cm. The powder is calendered into a dense, continuous, self-supporting positive electrode film with a porosity of 20%-40% and a thickness of 160-200 μm.
[0043] III. Negative Electrode Preparation: a) Add 940 g of hard carbon, 30 g of Super P and 30 g of PTFE powder to a high-speed shear mixer.
[0044] b) Fiberize at 1500 rpm for 6 minutes.
[0045] c) The negative electrode film is calendered using a two-roll press (parameters same as the positive electrode) to form a self-supporting negative electrode film.
[0046] IV. Battery Assembly: The positive electrode film is hot-pressed onto carbon-coated aluminum foil, and the negative electrode film is hot-pressed onto aluminum foil. After cutting and baking, they are assembled together with the separator, electrolyte, etc. into a soft pack or square cell.
[0047] The ceramic-coated membrane is a diaphragm. The electrolyte was a 1M NAPF6 DEC / PC (1:1 v / v) solution with 5% FEC and 2% PS additives.
[0048] Example 2
[0049] The procedure is the same as in Example 1, except that carbon-coated sodium ferric sulfate is mixed in a mass ratio of 7:3 between large particles with D50=10 μm and fine particles with D50=0.5 μm. All other steps and parameters are exactly the same.
[0050] Comparative Example 1: The procedure was followed as in Example 1, except that step a) of the positive electrode pre-composite was omitted during the preparation of the positive electrode. 900 g of graded carbon-coated sodium ferric sulfate, 50 g of Ketjen black, and 50 g of PTFE powder were directly added to a high-speed shear mixer, and the fiberization mixing was completed in one go at 2000 rpm for 5 minutes. Subsequent steps were the same.
[0051] Comparative Example 2: Follow the steps in Example 1, except that only D is used as the positive electrode active material. 50 Sodium ferric sulfate with a single carbon particle size of 8 μm was used, without particle size distribution. All other steps and parameters were exactly the same.
[0052] Comparative Example 3: A dry process was performed using a conventional wet binder. The positive electrode formulation was: 90 wt% sodium ferric sulfate, 5 wt% Ketjen black, and 5 wt% polyvinylidene fluoride (PVDF) powder. After simple mechanical mixing of all powders, a roll forming process was attempted, followed by the same subsequent steps.
[0053] Performance testing: Table 1: sample Preparation process Initial discharge specific capacity (mAh / g) 100-cycle capacity retention (%) Electrode mechanical strength Example 1 Pre-composite + graded + PTFE + low humidity 102 96.2% Excellent, no cracks Example 2 Pre-composite + graded + PTFE + low humidity 100 96.6% Excellent, no cracks Comparative Example 1 Conductive-free pre-composite 92 89.7% good Comparative Example 2 No particle size distribution 94 90.1% Poor quality, fragile Comparative Example 3 Using PVDF adhesive - - Extremely poor quality, unable to form a film. Charge-discharge tests were conducted at a rate of 0.5 C. The battery prepared by the dry electrode in Example 1 of this invention had an initial discharge specific capacity of 102 mAh / g and a capacity retention rate of 96.2% after 100 cycles.
[0054] Example 2 also exhibits higher initial discharge specific capacity and cycle retention rate, which are superior to existing technologies.
[0055] The electrode film prepared in Comparative Example 1 showed poor uniformity, with a small amount of conductive agent agglomerates visible to the naked eye. The electrode resistance was approximately 45% higher than that of Example 1. The assembled battery exhibited an initial discharge specific capacity of 92 mAh / g at 0.5C, but the capacity retention after 100 cycles was only 89.7%. These results indicate that without pre-composite bonding, the high specific surface area nano-conductive agent cannot be uniformly dispersed and effectively coated on the surface of the active material, leading to low conductive network efficiency and significantly deteriorated battery rate performance and cycle stability.
[0056] The positive electrode film obtained by calendering in Comparative Example 2 was significantly more brittle, and cracks easily appeared at the edges when peeled off from the roll mill. The electrode compaction density was about 15% lower than that of Example 1. The assembled battery had a lower volumetric energy density. During cycling, due to the poor stability of the electrode structure, the capacity decayed rapidly, with a capacity retention of only 90.1% after 100 cycles. Compared with Example 1, the results show that the lack of fine particles in the positive electrode material and the non-dense electrode microstructure affect the electrochemical performance and long-term stability.
[0057] The mixture in Comparative Example 3 could not be rolled into a continuous, self-supporting film; it pulverized immediately after calendering and could not be successfully used to form electrodes. This comparative example demonstrates that not all binders are suitable for dry processes, and that PTFE's unique fibrillation properties are key to forming a binder fiber network and imparting cohesion and film-forming properties to the dry powder mixture.
[0058] The above results demonstrate that the present invention successfully solved the processing problem of sodium ferric sulfate material, and the prepared battery exhibits excellent performance and high cycle stability, fully proving the effectiveness and advancement of the present invention.
Claims
1. A dry preparation method for sodium ferric sulfate positive electrode sheets, characterized in that... The method is as follows: Carbon-coated sodium ferric sulfate particles are mixed with a positive electrode conductive agent at high speed, and the resulting composite is then mixed with a positive electrode binder. The composite is then subjected to high-speed shearing and fiberization to obtain a dry electrode mixture. The dry electrode mixture is then rolled and calendered to obtain a positive electrode film. The carbon-coated sodium ferric sulfate particles are made of D 50 Large particles of 5-10 μm and D 50 It consists of fine particles of 0.5-2 μm in a mass ratio of 7:3 to 9:
1.
2. The method as described in claim 1, characterized in that... The carbon coating thickness of the carbon-coated sodium ferric sulfate particles is 2-20 nm.
3. The method as described in claim 1, characterized in that... The positive electrode conductive agent is at least one of Ketjen black, carbon nanotubes, and graphene.
4. The method as described in claim 1, characterized in that... The positive electrode binder is PTFE fine powder with a particle size of 100-500μm.
5. The method as described in claim 1, characterized in that... Based on the aforementioned carbon-coated sodium ferric sulfate particles, positive electrode conductive agent, and positive electrode binder, the mass percentage of each component is as follows: carbon-coated sodium ferric sulfate particles 85-93%, positive electrode conductive agent 3-8%, and positive electrode binder 4-7%.
6. The method as described in claim 1, characterized in that... The carbon-coated sodium ferric sulfate particles and the positive electrode conductive agent are mixed in a high-speed mixer at a speed of 2000~5000 rpm for 5~15 min.
7. The method as described in claim 1, characterized in that... The resulting composite is then mixed with a positive electrode binder and subjected to fiberization in a high-speed shear mixer at a speed of 1000-3000 rpm for 3-10 minutes.
8. The sodium ferric sulfate positive electrode sheet prepared by the method according to any one of claims 1 to 7.
9. The application of the sodium ferric sulfate positive electrode sheet as described in claim 8 in the preparation of sodium-ion batteries.
10. A sodium-ion battery, comprising the sodium ferric sulfate positive electrode as described in claim 8.