Sodium Ferric Hexacyanoferrate(II) Materials

Abstract

The present disclosure relates to a sodium ferric-hexacyanoferrate(II) material, the particles of which have a particle size D50 value in the range of 4 μm to 50 μm and a particle size of 0.1 m 2 / g~10m 2 The present invention relates to a sodium ferric hexacyanoferrate(II) material having a BET specific surface area in the range of 0.1 μm / g.

Description

[Technical field]

[0001] The present disclosure generally relates to sodium ferric-hexacyanoferrate(II) materials, methods for preparing sodium ferric-hexacyanoferrate(II) materials, electrodes including sodium ferric-hexacyanoferrate(II) materials, and battery cells including at least one electrode including sodium ferric-hexacyanoferrate(II) materials. [Background technology]

[0002] Lithium-ion based batteries dominate the rechargeable battery market. However, this technology suffers from, at least but not exclusively, the drawback of the relatively scarce resource of lithium. Although superior to previous generations of secondary battery technology, lithium-ion based batteries are not environmentally friendly and are expensive from a recycling perspective.

[0003] Sodium-ion batteries represent an attractive alternative to lithium batteries and are perhaps the most viable means of supporting renewable energy sources for load leveling and excess energy storage purposes. The performance of sodium-ion batteries depends on the properties of the electrode materials. The cathode material is one of the key factors limiting the applications of sodium-ion batteries.

[0004] Prussian blue analogue cathode materials stand out as promising cathode materials for use in sodium ion batteries. Prussian blue analogues have a unique crystal structure with an open three-dimensional framework and large interstitial voids, and are capable of storing sodium ions. Prussian blue analogues of particular interest herein have a high content of Na and a low content of H. 2 O. Sodium ferric hexacyanoferrate(II) materials have a white color and are often referred to as "Prussian white". Prussian white has the chemical formula Na 2 Fe 2 (CN)6 and negligible water content (<0.08 H 2 It is a Prussian blue analogue with the same structure as Prussian blue but with a fluorescein isomerase (F / fu).

[0005] Drying is particularly important when Prussian white is used as a cathode active material because any water present in the Prussian white structure must be removed in order for the material to fully utilize its capacity in a battery cell. The presence of water can adversely affect the electrochemical potential and cycling stability in battery cells containing Prussian white as a cathode material.

[0006] Prussian white materials have been found to have variability in stable working capacity and cycling stability. A key factor that has been identified is the effect of exposure to moisture in air on the electrochemical performance of Prussian white materials. It has been determined that exposure to moisture results in the loss of Na from the Prussian white structure, thus limiting the working capacity.

[0007] Therefore, the problem of moisture degradation still exists, and therefore there is a need to improve the capacity and moisture stability of Prussian white electrode materials. Summary of the Invention

[0008] In view of the above and other shortcomings of the prior art, it is an object of the present disclosure to provide improvements in the moisture stability and capacity fade of sodium ferric-hexacyanoferrate(II) electrode materials.

[0009] This and other objects of the present disclosure may be achieved by a sodium ferric-hexacyanoferrate material according to claim 1. Further embodiments are set out in the dependent claims, the following description and the drawings.

[0010] Accordingly, the present disclosure relates to a sodium ferric-hexacyanoferrate (II) powder material. The particles of the sodium ferric-hexacyanoferrate (II) material have a particle size D50 value in the range of 4 μm to 50 μm and a particle size of 0.1 μm. 2 / g~10m 2 / g.

[0011] Particle size distribution is measured by laser diffraction using Mie theory, utilizing a Malvern Mastersizer 3000 instrument with an attached Areo S normal venturi for powders. The size range was set to 0.1-3500 μm. Before analysis, samples were sieved through a 1 mm sieve.

[0012] Surface area (BET) of N at 77K 2 It is measured by adsorption using a high-speed specific surface area pore distribution analyzer (Micromeritics, ASAP, 2020) and is expressed in units of area per mass of sample (m 2 / g).

[0013] "Electrode" is intended to be broadly interpreted herein as an ion source member in various electrochemical devices, including, but not limited to, batteries, fuel cells, electrochemical devices, and sensors.

[0014] The present inventors have determined that the particle size D50 value is in the range of 4 μm to 50 μm and the particle size D50 value is in the range of 0.1 m 2 / g~10m 2It has been found that a sodium ferric-hexacyanoferrate material having a BET specific surface area in the range of 0.1 μm / g can improve the capacity of the sodium ferric-hexacyanoferrate material over time by reducing capacity fading (loss of Na), particularly degradation due to moisture, while maintaining high electrical conductivity. In other words, it has been found that the loss of sodium in the sodium ferric-hexacyanoferrate material limits the practical capacity, and that the sodium ferric-hexacyanoferrate material according to the present invention is prone to less Na loss and therefore less capacity loss when exposed to moisture.

[0015] The particles of the sodium ferric hexacyanoferrate powder material preferably have a particle size D50 value in the range of 7 μm to 50 μm and a particle size of 0.1 m 2 / g~10m 2 The resulting sodium ferricyanide hexacyanoferrate material can have a BET specific surface area in the range of 100 / g. It has been found that the resulting sodium ferricyanide hexacyanoferrate material provides improved stability in moisture and thus significantly reduced capacity loss over time.

[0016] The particle size D50 value of the sodium ferric-hexacyanoferrate(II) material may be in the range of 10 μm to 30 μm. The resulting sodium ferric-hexacyanoferrate(II) material has been found to provide improved stability in water and therefore significantly reduced capacity loss over time.

[0017] The particle size D50 value of the sodium ferric-hexacyanoferrate(II) material may be in the range of 15 μm to 25 μm. The resulting sodium ferric-hexacyanoferrate(II) material has been found to provide significantly improved stability in water and therefore significantly reduced capacity loss over time.

[0018] The BET specific surface area of ​​sodium ferric hexacyanoferrate(II) is 0.1 m 2 / g~5m2 / g. The BET specific surface area of ​​the sodium ferric hexacyanoferrate material may be in the range of 0.1 m 2 / g~5m 2 It has been found that a BET specific surface area in the range of 0.1 to 0.5 μm / g improves the stability of sodium ferric hexacyanoferrate(II) materials in moisture. Higher BET specific surface area sodium ferric hexacyanoferrate(II) materials can be exposed to more moisture, which can induce loss of Na and capacity loss over time.

[0019] The BET specific surface area of ​​sodium ferric hexacyanoferrate(II) is 0.1 m 2 / g~1m 2 / g. It has been found that the moisture stability of the sodium ferric-hexacyanoferrate(II) material is significantly improved.

[0020] The particle size D10 value of the sodium ferric hexacyanoferrate material may be in the range of 1 μm to 20 μm, preferably in the range of 1 μm to 15 μm. It has been found that a smaller number of particles having a particle size in the lower range of 1 μm to 20 μm, e.g. 1 μm to 15 μm, improves stability in water. Such sodium ferric hexacyanoferrate material may further have an improved or at least satisfactory electrical conductivity.

[0021] The particle size D90 value of the sodium ferric-hexacyanoferrate(II) material may be in the range of 10 μm to 600 μm, and preferably, the particle size D90 value of the sodium ferric-hexacyanoferrate(II) material may be in the range of 10 μm to 50 μm. It has been found that such a sodium ferric-hexacyanoferrate(II) material has a significantly improved stability in water of the sodium ferric-hexacyanoferrate(II) material.

[0022] Sodium iron (II)-hexacyanoferrate (II) materials can exhibit a cubic crystal form.

[0023] Preferably, the sodium iron (II)-hexacyanoferrate (II) material has the chemical formula Na 2-y Fe[Fe(CN) 6 ·m H 2 O (where y < 0.2 and 0 < m < 3).

[0024] Such Prussian white materials have a high sodium content and a high theoretical capacity (about 170 mAh / g). However, Prussian white materials have been found to have high variability in reported stable practical capacity and cycle stability. An important factor that has been identified is the effect of exposure to moisture in the air on the electrochemical performance of Prussian white materials.

[0025] As demonstrated in the examples section, the inventors have found that Prussian white materials having a particle size D50 value in the range of 7 μm to 50 μm and a BET specific surface area in the range of 0.1 m 2 / g to 10 m 2 / g according to the present disclosure provide particularly high moisture stability and, otherwise, low loss of Na to the moisture-sensitive material.

[0026] The present disclosure further provides a method for preparing a sodium iron (II)-hexacyanoferrate (II) material according to any one of the preceding claims, - acid decomposition of Na 4 Fe(CN) 6 *10H 2 O, where the H + to Fe ratio is in the range of 7:1 to 1:1, and the temperature is in the range of 50 °C to 120 °C during a period in the range of 0.1 hours to 30 hours, thereby obtaining a powder of Na 2-y Fe[Fe(CN) 6 *mH 2 O (where y is < 0.2 and m is from 0 to 3), the acid decomposition step; - isolating and drying the powder obtained, wherein the powder has a particle size D50 value in the range of 4 μm to 50 μm and a particle size of 0.1 μm 2 / g~10m 2 and b. isolating and drying the resulting crystalline cellulose having a BET specific surface area in the range of 1 / g.

[0027] The present inventors have achieved a particle size D50 value in the range of 4 μm to 50 μm and a particle size D value of 0.1 m 2 / g~10m 2 It has been found that it is possible to prepare in a simple and cost-effective manner sodium ferric-hexacyanoferrate (II) materials having a BET specific surface area in the range of 0.1 μm to 1 μm / g, which improves the stability of the electrode material in water and reduces capacity loss over time. In particular, it has been found that by controlling the amount of acid and the period of time for which the acid is added, as disclosed herein, the particle size of the material can be advantageously controlled and tailored to obtain sodium ferric-hexacyanoferrate (II) materials according to the present disclosure.

[0028] The separation process can be carried out by any known separation method in the art before drying and removing the water from the powder.

[0029] The temperature during the acid decomposition step may be in the range of 50°C to 100°C.

[0030] The pressure may be ambient or near ambient pressure.

[0031] It has been found that in processes where the temperature during the acid decomposition step is kept within the range of 50°C to 120°C, preferably within the range of 50°C to 100°C, and ambient pressure is maintained, no or very little corrosion of the reactor materials is observed.

[0032] The duration of the acidolysis step may be in the range of 3 hours to 24 hours, optionally in the range of 3 hours to 10 hours.

[0033] The duration of the acid decomposition step can be adapted depending on whether a high yield or a fast process is desired. The inventors have found that if the set time is within the range of the present disclosure and the process time is longer, the yield is higher. A faster process results in a higher material consumption, i.e. more material is needed to reach the same yield.

[0034] In the process of separating and drying the resulting powder, the powder may have a particle size D50 value in the range of 7 μm to 50 μm.

[0035] The acids used in the acid decomposition process are hydrochloric acid (HCl), citric acid, formic acid, ascorbic acid, acetic acid, sulfuric acid, hydroiodic acid (HI), hydrobromic acid (HBr), and nitric acid (HNO 3 ), phosphoric acid (H 3 PO 4 ) Preferably, the acid in the acid decomposition step is a reducing acid.

[0036] H + The ratio of H to Fe may be in the range of 5:1 to 1:1. + It has been found that an Fe to Fe ratio in the range of 5:1 to 1:1 reduces particle etching, resulting in improved yield and reduced manufacturing costs.

[0037] H + The Fe ratio may be within the range of 3:1 to 1:1.

[0038] In a further aspect, the present disclosure relates to an electrode comprising the sodium ferric-hexacyanoferrate material according to the present disclosure.

[0039] In a further aspect, the present disclosure relates to a battery cell comprising at least one electrode according to the present disclosure, the electrode forming a positive electrode and a sodium source within the battery cell.

[0040] Several illustrative embodiments will now be described with reference to the accompanying drawings. [Brief description of the drawings]

[0041] [Figure 1] SEM images of sodium iron(II)-hexacyanoferrate(II) materials having different particle sizes (D50) according to the comparative examples and the present disclosure are shown. [Diagram 2] A diagram schematically showing a battery cell according to the present disclosure. [Diagram 3] A diagram schematically showing two alternative methods for preparing a sodium iron(II)-hexacyanoferrate(II) material according to the present disclosure. [Figure 4] A graph showing the comparison results of a 5-day cycle test of four sodium iron(II)-hexacyanoferrate(II) materials according to the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

[0042] The sodium iron(II)-hexacyanoferrate(II) material according to the present disclosure generally has the formula (Na 2-y Fe[Fe(CN) 6 .mH 2 O) (where y < 0.2 and 0 < m < 3), which is generally called Prussian white.

[0043] The sodium iron(II)-hexacyanoferrate(II) material has a particle size D50 value in the range of 4 μm to 50 μm and a BET specific surface area in the range of 0.1 m 2 / g to 10 m 2 / g. The inventors have found that such sodium iron(II)-hexacyanoferrate(II) materials are more stable in water and thus show a reduction in the decrease of capacity over time when exposed to moisture. Optionally, the sodium iron(II)-hexacyanoferrate(II) material has a particle size D50 value in the range of 7 μm to 50 μm.

[0044] Figure 1 shows SEM images of sodium ferric-hexacyanoferrate material of different particle sizes. In image a) the particles have a particle size (D50) of 4.8 μm (D10 of 2 μm, D90 of 275.6 μm), in image b) the particles have a particle size (D50) of 6.3 μm (D10 of 3.8 μm, D90 of 548.3 μm), in image c) the particles have a particle size (D50) of 19.5 μm (D10 of 10.2 μm, D90 of 32.6 μm) and in image d) the particles have a particle size (D50) of 20.5 μm (D10 of 11.8 μm, D90 of 33.3 μm). 2 When measured using a high-speed surface area pore distribution analyzer (Micromeritics, ASAP, 2020) using adsorption, the BET specific surface area of ​​sample a) and sample b) was 1.97 m 2 / g~1m 2 / g, and the BET specific surface area of ​​sample c) and sample d) is 0.97 m 2 / g~0.61m 2 / g.

[0045] 2 shows a schematic principle of a sodium battery with electrodes including sodium ferric-hexacyanoferrate material according to the present disclosure, forming a positive electrode and a sodium source 100 utilizing sodium ions 101 as charge carriers. Sodium batteries store energy in chemical bonds in the negative electrode 102. When the battery 100 is charged, Na + Ions 101 are deintercalated from the positive electrode 103 and move towards the negative electrode 102. During discharge, the process is reversed. When the circuit is completed, electrons move back from the negative electrode 102 to the positive electrode 103, transferring Na + The ions 101 return to the positive electrode 103. During discharge of the battery cell, oxidation occurs at the negative electrode 102 and reduction occurs at the positive electrode 103, as shown in Figure 1. The flow of current is determined by the potential difference between the positive electrode 103 and the negative electrode 102, the cell voltage.

[0046] The two electrodes are separated by an electrolyte 104, for example 1M NaPF6-EC:DEC.

[0047] As used herein, the term "battery" means a device that contains one or more battery cells.

[0048] In an "electrochemical cell" chemical energy is converted into electricity by reduction and oxidation (redox) reactions at electrodes.

[0049] Thus, the positive electrode material is represented by the formula (Na 2-y Fe[Fe(CN) 6 ].mH 2 O) where y is <0.2.

[0050] The electrical conductivity combined with the good rate capability of the cathode material allows for rapid charging and discharging.

[0051] The negative electrode material is not particularly limited as long as it is a material capable of storing / releasing sodium, and examples thereof include metal composite oxides, sodium metal, sodium alloys, silicon, silicon-based alloys, tin-based alloys, bismuth-based alloys, metal oxides, conductive polymers such as polyacetylene, Na-Co-Ni-based materials, and hard carbon.

[0052] The battery cell may further comprise a separator 105 to prevent electrical shorts between the negative and positive electrodes and to provide mechanical stability to the cell. The separator material may be any chemically stable, electrically insulating material, such as a polymer film, typically made from polypropylene, polyethylene, or a combination thereof.

[0053] The method according to the present invention for producing Prussian white material for a sodium battery as shown in FIG. 1 is shown in FIG. 3. In method 1, Na 4 Fe(CN) 6 *10H 2 The acid decomposition process of O, wherein H + The ratio of Fe is in the range of 7:1 to 1:1, and the temperature is in the range of 50°C to 120°C for a period of time in the range of 0.1 hours to 30 hours, whereby the compound of the formula Na2-y Fe[Fe(CN) 6 ]*mH 2 The method includes (A) an acid decomposition step to obtain a powder of 1,2-dichloro-1,2,3-tetrafluoroethylene (1,2,3,4-tetrafluoroethylene), and (B) a step of isolating and drying the obtained powder. The difference between the method 2 and the method 1 is that the water and Na 4 Fe(CN) 6 *10H 2 The mixture of 1,000 and 1,000 sieves was heated before adding the acid. 2 / g~10m 2 Powder having a BET specific surface area in the range of 1 / g.

[0054] In method 2, the reaction is carried out by acidic NaCl precipitation, for example with HCl. 4 Fe(CN) 6 *10H 2 It starts with the acid decomposition of O, where H + The Fe ratio is in the range of 7:1 to 1:1. The temperature is maintained in the range of 50° C. to 120° C. for a period in the range of 0.1 hours to 30 hours.

[0055] Alternatively, the acid may be citric acid, formic acid, ascorbic acid, acetic acid, sulfuric acid, hydroiodic acid (HI), hydrobromic acid (HBr), nitric acid (HNO 3 ), phosphoric acid (H 3 PO 4 The reaction mixture is then cooled to room temperature (RT) and filtered in air.

[0056] Further steps can include forming an electrode comprising the Prussian white powder according to the present disclosure. The electrode is prepared by conventional slurry casting, in which the Prussian white powder prepared according to the present disclosure is mixed with conductive additives, binders and solvents in a ball mill. The slurry is then deposited on a current collector, and the film thickness is controlled by doctor blade method. One or more electrodes comprising the Prussian white powder are placed in a battery cell to form a high-voltage, high-capacity and moisture-resistant positive electrode(s).

[0057] Devices similar to the electrodes described above, such as fuel cell electrodes, may advantageously include Prussian white powder according to the present disclosure produced in accordance with the present disclosure.

[0058] Experimental Data Example 1: Preparation of Prussian Blue Analogue Electrode Material Using the methods described above and following the steps shown in FIG. 3, Prussian white can be synthesized to produce preferred particle sizes according to the present disclosure.

[0059] Example 2: Comparative study of the cycling stability of Prussian blue analogue powders with different particle sizes and BET specific surface areas The resulting powder is mixed with the solvent, conductive additive and binder by milling, e.g., ball milling, for 1 hour. The solvent can be any type of solvent known to those skilled in the art. The conductive additive can be any type of conductive additive known to those skilled in the art. For example, various types of carbon compounds, e.g., Super P, C65, C45, carbon black, e.g., Ketjen Black, can be utilized. The binder is not limited to a specific binder. For example, alginate, carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR), polyvinylidene fluoride (PVdF) can be used. The resulting slurry is then coated on a metal foil and evenly distributed by a doctor blade. The solvent is removed from the electrodes at 80° C. for 30 minutes and transferred to either an inert reservoir (reference sample) or a storage container (exposed sample) at 75% RH for 5 days. All electrodes are then dried at 120° C. for 12 hours. The capacity loss presented is the relative difference between the reference sample and the exposed sample.

[0060] In conclusion, the samples according to the present disclosure clearly show a surprising reduction in Na loss and therefore improved moisture stability compared to the comparative samples with smaller particle size.

Claims

1. A sodium iron(II)-hexacyanoferrate(II) material, wherein the particles of the sodium iron(II)-hexacyanoferrate(II) material have a particle size D50 value within the range of 4 μm to 50 μm and a BET specific surface area within the range of 0.1 m ２ / g to 10 m ２ / g, and the particle size D50 and the BET specific surface area are determined according to the method disclosed in this specification, the sodium iron(II)-hexacyanoferrate(II) material.

2. 2. The sodium ferric hexacyanoferrate material of claim 1, wherein the particle size D50 value is in the range of 7 μm to 50 μm.

3. 2. The sodium ferric hexacyanoferrate material of claim 1, wherein the particle size D50 value is in the range of 10 μm to 30 μm.

4. 2. The sodium ferric hexacyanoferrate material of claim 1, wherein the particle size D50 value is in the range of 15 μm to 25 μm.

5. The BET specific surface area is 0.1 m ２ / g to 5m ２ 2. The sodium ferric-hexacyanoferrate material of claim 1, wherein the iron content is in the range of 0.1 wt. / g.

6. The BET specific surface area is 0.1 m ２ / g to 1m ２ 2. The sodium ferric-hexacyanoferrate material of claim 1, wherein the iron content is in the range of 0.1 wt. / g.

7. 2. The sodium ferric hexacyanoferrate material of claim 1, wherein the particle size D10 value is in the range of 1 μm to 20 μm.

8. 2. The sodium ferric hexacyanoferrate material of claim 1, wherein the particle size D10 value is in the range of 1 μm to 15 μm.

9. 2. The sodium ferric hexacyanoferrate material of claim 1, wherein the particle size D90 value is in the range of 10 μm to 50 μm.

10. 2. The sodium ferric-hexacyanoferrate material of claim 1, which is in cubic crystalline form.

11. Formula Na ２－ｙ Fe[Fe(CN) ６ ]m H ２ 2. The sodium iron(II)-hexacyanoferrate(II) material of claim 1, having the formula: O, where y<0.2 and 0<m<3.

12. A method for preparing the sodium iron(II)-hexacyanoferrate(II) material of claim 1, comprising: -Na in acid ４ Fe(CN) ６ *10H ２ Acid decomposition of O, where H ＋ The ratio of Na to Fe is in the range of 7:1 to 1:1, and the temperature is in the range of 50°C to 120°C for a period of time in the range of 0.1 hours to 30 hours, whereby Na ２－ｘ Fe[Fe(CN) ６ ]*mH ２ an acid decomposition step to obtain a powder of 0, wherein x is <0.2 and m is 0-3; - A step of separating and drying the obtained powder, wherein the powder has a particle size D50 value within the range of 4 μm to 50 μm and a BET specific surface area within the range of 0.1 m ２ / g to 10 m ２ / g, and separating and drying the powder; A method comprising:

13. 13. The method for preparing sodium ferric-hexacyanoferrate material of claim 12, wherein the temperature during the acid decomposition step is in the range of 50°C to 100°C.

14. 13. The method for preparing sodium ferric-hexacyanoferrate material of claim 12, wherein the duration of the acid decomposition step is in the range of 3 hours to 24 hours, optionally in the range of 3 hours to 10 hours.

15. The acid in the acid decomposition step is hydrochloric acid (HCl), citric acid, formic acid, ascorbic acid, acetic acid, sulfuric acid, hydroiodic acid (HI), hydrobromic acid (HBr), nitric acid (HNO ３ ), phosphoric acid (H ３ P.O. ４ 13. The method for preparing sodium ferric-hexacyanoferrate material of claim 12, wherein the sodium ferric-hexacyanoferrate material is any one of

16. The H ＋ 13. The method for preparing sodium ferric-hexacyanoferrate material of claim 12, wherein the ratio of sodium to Fe is in the range of 5:1 to 1:

1.

17. An electrode comprising the sodium iron(II)-hexacyanoferrate(II) material of claim 1.

18. 20. A battery cell comprising at least one electrode according to claim 17, wherein the electrode forms a positive electrode and a source of sodium or potassium within the battery cell.

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