Cathode material comprising iron hydroxyfluoride

Abstract

The invention relates to a method for producing a cathode active material, comprising at least partially dissolving iron fluoride trihydrate (IFH) in a polar solvent, thereby obtaining a solution; adding water to the solution, thereby precipitating a compound comprising pyrochlore hydrated iron hydroxyfluoride (Pyr-IHFH); separating the precipitated compound from the solution; and heating the separated precipitated compound to a temperature of 50-400 DEG C, thereby obtaining a cathode active material comprising pyrochlore iron hydroxyfluoride (Pyr-IHF) wherein water is added to the solution to convert the IFH into Pyr-IHFH. The invention further relates to a cathode active material comprising Pyr-IHF, a cathode comprising the cathode active material and a battery comprising the cathode.

Description

[0001] Technical field of the present invention

[0002] The present invention relates to a method for producing a cathode active material, and further relates to the cathode active material, a cathode and a battery comprising the cathode active material.

[0003] background

[0004] When looking at stationary batteries, a key challenge involves achieving extended service life and reliability at a reasonable cost. Stationary batteries play a key role in the integration of renewable energy sources, which require long-term performance and minimal degradation over multiple charge-discharge cycles. Developing durable battery technology that can withstand frequent use without significant capacity loss is a challenge, especially when considering the economic constraints associated with stationary energy storage projects. Therefore, there is a need for low-cost but high-performance secondary (i.e., rechargeable) batteries in general, and stationary secondary batteries in particular.

[0005] Iron fluoride-based compounds, including iron(III) fluoride, iron(III) hydroxyfluoride, iron(III) oxyfluoride, and iron(III) hydroxyoxyfluoride, are promising cathode active materials for rechargeable batteries, especially lithium-ion batteries (LIBs), due to the abundance and cost-effectiveness of iron. These compounds exhibit favorable electrochemical properties, providing high theoretical capacity, high oxidative stability, and stable cycling, and also offer high lithiation potential for LIBs.

[0006] Rhombohedral iron trifluoride with a hierarchized microporous / mesoporous texture from gaseous fluorination of iron disilicide Delbègue, Guérin et al., E3S Web of Conferences 16, 08001 (2017) disclose stable low-temperature r-FeF3 for use in cathodes for LIBs, wherein the r-FeF3 has hierarchical pores in a mesoporous / microporous structure that is conducive to lithium diffusion. Rhombohedral iron (III) trifluoride is obtained by fluorination of iron disilicide in pure fluorine gas.

[0007] It is known that the direct fluorination process requires the use of highly toxic, hazardous fluorinating agents and is therefore considered a hazardous process.

[0008] Chemistry and key structural features of oxyhydroxy-fluorides: relationships with the acidic character, thermal stability and surface area Demourgues, Francke et al., Journal of Fluorine Chemistry, Vol. 114, No. 2 (2002), pp. 229-236 disclose hydroxyferric fluoride having a hexagonal tungsten bronze (HTB) type structure. The HTB type structure provides a small cavity suitable for adsorption of small molecules such as pyridine and ammonia.

[0009] However, this HBT type structure may undergo short-range structural changes in lithium-ion batteries, which reduce lithium-ion diffusion capabilities and thus degrade cathode and battery performance.

[0010] A new form of FeF 3 with the pyrochlore structure: Soft chemistry synthesis, crystal structure, thermal transitions and structural correlations with the other forms of FeF 3 De Pape and Ferrey, Materials Research Bulletin, Vol. 21, No. 8 (1986), pp. 971-978, disclose iron (III) trifluoride having a cubic pyrochlore crystal structure (Pyr-FeF3). The cubic pyrochlore structure provides a large cavity formed by corner-sharing FeF6 octahedra. The pyrochlore crystal structure (Pyr-FeF3) is capable of absorbing and desorbing small molecules such as ammonia.

[0011] A disadvantage of Pyr-FeF3 is that battery cells including cathodes containing Pyr-FeF3 as the active material tend to have low or limited rate capabilities.

[0012] Synthesis by Thermal Decomposition of Two Iron Hydroxyfluorides: Structural Effects of Li Insertion , K. Lemoine, L. Zhang et al., Chem. Mater. 2019, 31, 11 (2019), pp. 4246-4257 discloses Fe 2+ Fe 3+ F5(H2O)2 and Fe 2+ Fe2 3+ The thermal decomposition of F8(H2O)2 under ambient air synthesized ferric hydroxyfluoride, in which both pyrochlore and HTB type structures were present. The capacity was excellent but showed a significant drop after the first charge / discharge cycle, which resulted in a capacity of about 110 mAh g -1 This decrease is believed to be related to the amorphization of the pyrochlore network and the transformation of the HTB phase into a ReO3 type phase.

[0013] A disadvantage of this cathode active material is that its use in secondary batteries is limited, since the capacity decreases significantly after only one charge / discharge cycle due to structural deformation.

[0014] Another disadvantage of the aforementioned methods is that they require the use of expensive, often hazardous and toxic compounds, which makes the cathode active material also expensive.A further advantage of the aforementioned methods is that they allow limited control over the morphology of the produced cathode active material, thereby resulting in non-uniform properties.

[0015] Therefore, there is a need for a cheaper, safer and more environmentally friendly method of producing ferric fluoride-based cathode active materials, especially in combination with keeping the cost of these cathode active materials low while maintaining high and uniform performance when used in cathodes in batteries. SUMMARY OF THE INVENTION

[0017] The present invention aims to overcome one or more of the aforementioned disadvantages. It is an object of the present invention to provide a method for producing cathode active materials that does not require the use of hazardous or toxic compounds. Another object is to provide a cheaper method that is more environmentally friendly than methods known in the prior art. A further object is to provide a method that allows for control of the morphology of the produced cathode active material to improve the performance of the cathode active material, in particular the rate capability and cycling stability.

[0018] Another object of the present invention is to provide a cathode active material for a cathode which is cheaper than the materials known in the prior art while having properties such as electrochemical performance and stability which are at least as good as those known in the prior art, and which may be even better.

[0019] Another object is to provide cathodes and batteries that are cheaper than those known in the prior art while having the same or even better performance, in particular with respect to lifetime, repeated charge / discharge of the battery (ie cycling stability) and rate capability.

[0020] According to a first aspect of the present disclosure, there is provided a method of producing a cathode active material as described in the accompanying claims.

[0021] The method includes preparing a solution comprising a polar solvent and ferric fluoride trihydrate (FeF3.3H2O, abbreviated as IFH). IFH is at least partially dissolved in the polar solvent. Advantages of using IFH as a precursor include that it is an inexpensive and commercially available compound.

[0022] By "at least partially dissolved" is meant that at least 10%, preferably at least 20%, more preferably at least 50%, most preferably at least 60%, e.g. at least 70%, at least 80%, at least 85%, at least 90% or substantially all of the IFH is dissolved in the polar solvent.

[0023] The method further comprises precipitating a compound comprising or consisting essentially of hydrated ferric hydroxyfluoride (Pyr-IHFH).Precipitation is achieved by adding water to the solution, thereby converting the (dissolved) IFH in the solution to Pyr-IHFH.

[0024] The precipitated compound comprising or consisting essentially of Pyr-IHFH can then be separated from the solution. The precipitated compound can be separated from the solution by separation techniques known in the art, such as filtration, decantation, or centrifugation.

[0025] In the next step, the separated precipitated compound is dried at a temperature of 20-400°C, preferably 50-400°C, more preferably 100-300°C, such as 200-280°C, to obtain the cathode active material. The cathode active material comprises or consists essentially of pyrochlore ferric hydroxyfluoride (Pyr-IHF). In other words, drying removes at least some, and essentially all, water molecules from Pyr-IHF, to obtain Pyr-IHF.

[0026] Advantageously, the precipitated compound is dried by heating the precipitated compound to a temperature of 100-400° C. at atmospheric pressure, preferably 200-300° C. at atmospheric pressure, more preferably 250-280° C. at atmospheric pressure. It will be appreciated that when drying is carried out under reduced pressure, the temperature required to obtain the same degree of water removal, and therefore conversion of Pyr-IHFH to Pyr-IHF, will be lower than when drying is carried out at atmospheric pressure.

[0027] Advantageously, the ratio of the weight of IFH in the solution to the volume of the polar solvent is 0.002-0.1 g / mL, preferably 0.003-0.05 g / mL, more preferably 0.005-0.05 g / mL.

[0028] Advantageously when water is added to the solution, 1-15 vol%, preferably 1.5-10 vol%, more preferably 2-5 vol%, such as 3 or 4 vol% water is added to the solution based on the volume of the polar solvent in the solution.

[0029] Advantageously, the polar solvent is one or more of an alcohol, ethylene glycol, glycerol or an acid. Non-limiting examples of suitable alcohols include ethanol, methanol or isopropanol. A preferred polar solvent is ethanol.

[0030] Advantageously, the Pyr-IHFH contained in the precipitation compound has a cubic pyrochlore structure. Advantageously, the Pyr-IHFH comprises pores having an average diameter of 2.5-5 Å, more preferably 3-4 Å, such as 3-3.8 Å, as calculated by X-ray diffraction (XRD) analysis.

[0031] Advantageously, the pores of the IHFH are at least partially filled with water molecules.

[0032] According to a second aspect of the present disclosure, there is provided a cathode active material as described in the accompanying claims.

[0033] The cathode active material comprises or consists essentially of pyrochlore ferric hydroxyfluoride (Pyr-IHF). Advantageously, the cathode active material is obtained, ie manufactured or produced, by means of the method of the first aspect of the present disclosure.

[0034] Advantageously, the Pyr-IHF contained in the cathode active material comprises pores having an average diameter of 2.5-5 Å, more preferably 3-4 Å, such as 3-3.8 Å, as calculated by XRD analysis.

[0035] Advantageously, the cathode active material comprises or consists essentially of particles, wherein the particles comprise or consist essentially of Pyr-IHF. Advantageously, the particles comprising or consisting essentially of Pyr-IHF have an average diameter calculated by transmission electron microscopy (TEM) analysis of 100-500 nm, preferably 150-400 nm, more preferably 175-300 nm, such as 200-250 nm.

[0036] According to a third aspect of the present disclosure, there is provided a cathode as described in the accompanying claims.

[0037] The cathode comprises the cathode active material of the second aspect of the disclosure.

[0038] Advantageously the cathode further comprises carbon nanotubes (CNTs).

[0039] According to a fourth aspect of the present disclosure, there is provided a battery comprising the cathode of the third aspect of the present disclosure and thus comprising the cathode material of the second aspect of the present disclosure.

[0040] Advantageously, the battery is a secondary battery. Advantageously, the battery is a lithium-ion battery.

[0041] Description of the drawings

[0042] Aspects of the present invention will now be described in more detail with reference to the accompanying drawings, in which like reference numerals indicate like features and in which:

[0043] - Figure 1 Schematic representation of the method of the present invention;

[0044] - Figure 2 shows the SEM image of Pyr-IHFH;

[0045] - Figure 3A and 3B TEM images of Pyr-IHFH at different magnifications are shown;

[0046] - Figure 4 shows an SEM image of Pyr-IHF;

[0047] - Figure 5A and5B TEM images of Pyr-IHF at different magnifications are shown;

[0048] - Figure 6 shows the particle size distribution (PSD) of the cathode active material of the present invention;

[0049] - Figure 7A shows the HAADF STEM image of Pyr-IHFH, and Figure 7B and 7C Shows HAADF STEM images of Pyr-IHF at different magnifications;

[0050] - Figure 8A and 8B X-ray absorption spectroscopy (XAS) analysis of Pyr-IHFH and Pyr-IHF in the X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) regions are shown, respectively;

[0051] - Figure 9A and 9B Showing the charge and discharge voltage curves of the battery of the present invention with different electrolytes at a medium current rate;

[0052] - Figure 10 The results show that the battery of the present invention with different electrolytes has a AM The charge and discharge capacity and coulombic efficiency measured at a current density of up to 250 charge / discharge cycles;

[0053] - Figure 11 The battery of the present invention is shown to be 25-1000mA / g AM The rate performance measured at different current densities;

[0054] - Figure 12 Another battery of the present invention is shown to be 0.1A / g AM The charge and discharge voltage curves measured at a current density of ;

[0055] - Figure 13A and 13B The two batteries of the present invention are shown to be AM Charge and discharge voltage curves at high density;

[0056] - Figure 14 The battery of the present invention is shown to be 1A / g AM The charge and discharge capacity and coulombic efficiency of the device were improved up to 1000 charge / discharge cycles at high current density. Detailed Description of the Invention

[0058] Figure 1A method for producing a cathode active material is schematically shown, wherein the cathode active material comprises or consists essentially of pyrochlore ferric hydroxyfluoride (Pyr-IHF).

[0059] Method 1 includes operation 2 of preparing a solution, operation 4 of precipitating a compound, operation 5 of isolating the precipitated compound, and operation 6 of drying the precipitated compound. Method 1 further optionally includes operation 3 of separating any undissolved precursor from the solution.

[0060] The solution comprises a precursor at least partially dissolved in a polar solvent. The precursor is ferric fluoride trihydrate (FeF3.3H2O, abbreviated as IFH).

[0061] Advantageously, the polar solvent is a liquid alcohol, preferably ethanol.

[0062] IFH can be dissolved in the polar solvent by means known in the art. Preferred embodiments include stirring the polar solvent to dissolve at least a portion of the IFH, wherein the polar solvent is at a temperature of 20-40°C, such as room temperature. It will be appreciated that the temperature should be kept below the evaporation temperature of the polar solvent to prevent it from being removed from the (liquid) solution.

[0063] Optionally, the method includes a removal operation 3 in which any undissolved precursor is removed from the solution. Removal can be performed by methods known in the art, such as centrifugation and decantation, filtration, or vacuum drying. This allows the waste of IFH to be minimized, thereby making the method of the present disclosure more environmentally friendly.

[0064] A compound is then precipitated in the solution by adding water to the solution. The precipitated compound comprises or consists essentially of hydrated ferric hydroxyfluoride (Pyr-IHFH). In other words, adding water to the solution converts at least a portion of the dissolved IFH into Pyr-IHFH.

[0065] The inventors surprisingly found that the synthesis method can be carried out over the entire pH range. Advantageously, the water has a pH of 4 to 10, more preferably 6 to 7. Advantageously, the water is distilled water.

[0066] After precipitation the precipitated compound is separated from the solution during a separation operation 5. The separation can be carried out by methods known in the art, such as centrifugation and decantation and / or filtration.

[0067] Advantageously, the Pyr-IHFH is present in the precipitation compound as particles, ie, particles comprising or consisting essentially of Pyr-IHFH.

[0068] Advantageously the particles have an average diameter calculated from TEM analysis of 200-250 nm. Advantageously the particles are substantially spherical.

[0069] Advantageously, pyrochlore IHFH has a cubic pyrochlore structure. Within the pyrochlore structure of IHFH, the Fe(III) ion is surrounded by six anionic F / OH ligands at the same site 48f (mixed occupancy). The iron octahedra are corner-sharing, forming 3D interconnected hexagonal channels aligned with the

[110] direction and equivalent directions.

[0070] Advantageously, the diameter of the pores in Pyr-IHFH is calculated from XRD analysis to be 3-4 Å, such as 3.8 Å. Advantageously, the pores have a substantially hexagonal cross-section. Advantageously, the average diameter of the substantially hexagonal pores is defined as the distance between the pair of opposing F / OH ligands having the shortest distance between them, projected onto a plane perpendicular to the direction of pore propagation, i.e., the

[110] direction or an equivalent direction.

[0071] Drying operation 6 advantageously involves removing at least a portion, and substantially all, of the water molecules present in the precipitated compound, particularly within the pores of Pyr-IHFH. Therefore, the drying temperature is selected to allow for the removal of water molecules. For example, when drying operation 6 is performed at atmospheric pressure, the temperature is advantageously at least 100° C., preferably 200-300° C., for example 250-280° C. It should be understood that when heating operation 6 is performed under reduced pressure, the drying temperature can also be correspondingly lowered to achieve the same result.

[0072] The drying operation can be carried out by techniques and heating equipment known in the art, for example in a tube furnace.

[0073] Advantageously, the precipitation compound is heated to the predetermined drying temperature at a heating rate of 0.001-100°C / min, preferably 0.1-50°C / min, more preferably 1-25°C, for example 5-10°C / min.

[0074] Advantageously, the precipitated compound is cooled to room temperature at a cooling rate of 0.001-100°C / min, preferably 0.1-50°C / min, more preferably 1-25°C, for example 5-10°C / min, for example at a natural cooling rate.

[0075] Advantageously, the precipitated compound is dried for a duration of 1-120 minutes, preferably 5-60 minutes, more preferably 10-45 minutes, such as 20-30 minutes. "Drying duration" in the present disclosure means the time during which the precipitated compound is dried once the predetermined drying temperature has been reached, i.e. excluding any heating and cooling time.

[0076] Alternatively or additionally, but advantageously, the precipitated compound can be dried by means of supercritical fluid extraction, for example using, but not limited to, supercritical CO 2 (scCO 2 ). Advantageously, when drying is performed by supercritical fluid extraction, the drying temperature can be as low as room temperature.

[0077] A cathode active material is obtained after completion of the drying operation 6. The cathode active material comprises or consists essentially of pyrochlore ferric hydroxyfluoride (Pyr-IHF).

[0078] Advantageously, Pyr-IHF is present in the cathode as particles, i.e., particles comprising or consisting essentially of Pyr-IHF. Advantageously, the particles comprising or consisting essentially of Pyr-IHF have substantially the same average diameter and shape as the particles comprising or consisting essentially of Pyr-IHFH.

[0079] Advantageously, particles comprising or consisting essentially of Pyr-IHF have an average diameter of 200-250 nm as calculated from TEM analysis. More specifically, the particle diameter is determined by approximating the area of ​​the particle to an ellipsoid and then calculating the diameter of the area equivalent circle.

[0080] Advantageously, the particles are substantially spherical. Substantially spherical in the present disclosure means a spherical or nearly spherical shape, such as an ellipsoid, wherein the lengths of the three axes defining the ellipsoid do not differ from each other by more than 20%.

[0081] Advantageously the particles have a narrow particle size distribution (PSD) calculated from the particle diameters calculated by TEM analysis. Advantageously the PSD has a d equal to or less than 210 nm. 10 value, equal to or less than 240nm d 25 value, equal to or less than 265nm d 50 value, equal to or less than 300nm d 75 value and d equal to or less than 325nm 90 One or more of the values.

[0082] d x A value of d = d 265 nm means that x% of the particles have a size equal to or smaller than that value. For example, for the cathode active material of the present invention, a particle size equal to or smaller than d 265 nm is 50 The value means that 50% of the particles have a value equal to or less than 265 nm.

[0083] Advantageously, the Pyr-IHF comprises pores, i.e., 3D interconnected pores. Advantageously, the pores are formed by the corner-sharing FeF 6-x (OH) x The diameter of the pores in Pyr-IHF is advantageously 3-4 Å, such as 3.8 Å, as calculated by XRD analysis.

[0084] Advantageously, the Pyr-IHF further comprises pores within the particles. Advantageously, the pores have an average diameter of 1-5 nm as shown by TEM analysis.

[0085] The inventors surprisingly discovered that the method of the present disclosure allows the obtained particles to have a well-controlled morphology - in particular the presence of pores and the shape of the particles - as well as an average diameter and a narrow particle size distribution that are considered to be optimal for preparing cathodes using the cathode active material. Prior art methods generally result in particles with a large particle size distribution, which indicates a lack of uniformity. In addition, the particles obtained using the prior art methods generally have an average diameter of less than 50 nm or in the micrometer range. However, it is known that particles with an average diameter of less than 50 nm lead to excessive CEI formation, while particles in the micrometer range generally lead to poor electron or ion diffusion.

[0086] The present invention further relates to a cathode comprising Pyr-IHF as cathode active material.

[0087] Advantageously, the cathode further comprises a conductive compound, which may be any conductive compound suitable for cathodes known in the art. Particularly preferred, but non-limiting, examples of conductive compounds include carbon black, CNTs, and graphene. Alternatively or additionally, but also alternatively, the conductive compound is a carbon coating applied to the surface of the active material (Pyr-IHF).

[0088] The inventors surprisingly discovered that when CNTs are added to the conductive compound and thus to the cathode, the overall capacity of the battery comprising the cathode can be improved. Furthermore, the coulombic efficiency can be improved, even exhibiting values ​​close to 100% after repeated charging and discharging.

[0089] Without wishing to be bound by any theory, the inventors believe that CNTs improve the electronic conductivity within the conductive network of the cathode, thereby improving the reversible capacity of the material.

[0090] Advantageously the cathode further comprises a cathode current collector which may be any cathode current collector known in the art.

[0091] The present invention further relates to a battery, in particular a lithium-ion battery, comprising a cathode according to the invention. Advantageously, the (lithium-ion) battery is a secondary (lithium-ion) battery.

[0092] The battery further comprises an anode. The anode can be any anode known in the art. Advantageously, the anode comprises an anode current collector which can be any anode current collector known in the art.

[0093] The battery further comprises an electrolyte. The electrolyte may be a liquid electrolyte or a solid electrolyte. The electrolyte may be any electrolyte known in the art, such as a lithium lanthanum zirconium oxide (Li7La3Zr2O 12 , LLZO) electrolyte, which is optionally doped, ionic liquid electrolytes, sulfide electrolytes and conventional carbonate electrolytes. Non-limiting examples of suitable electrolytes include LLZO, doped LLZO, LiPF6-ethylene carbonate (EC) / dimethyl carbonate (DMC) (conventional carbonate electrolyte), lithium bis(fluorosulfonyl)imide (LiFSI) in EC / DMC, LiFSI in dimethyl ether (DME), 1-butyl-1-methylpyrrolidone in bis(trifluoromethanesulfonyl)imide (Pyr 1,4 TFSI) in lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) (ionic liquid electrolyte), in Pyr 1,4 LiFSI in TFSI, 1-propyl-1-methylpyrrolidine bis(trifluoromethanesulfonyl)imide (Pyr 1,3 LiFSI in TFSI).

[0094] The battery may further include a separator, especially when the electrolyte is a liquid electrolyte. The separator may be any separator known in the art, such as a glass fiber separator.

[0095] Without wishing to be bound by any theory, the inventors believe that ion diffusion in the cathode, particularly lithium ion diffusion when the battery is a lithium ion battery, occurs by diffusion through the pores of Pyr-IHF in the cathode.

[0096] Advantageously, the presence of nanoscale pores (1-5 nm, according to TEM analysis) in the Pyr-IHF particles further allows for improved electrochemical performance of the battery. The inventors believe this is because the electrolyte, for example, containing lithium ions when the battery is a lithium-ion battery, can penetrate into the pores of the Pyr-IHF, thereby reducing ion diffusion paths.

[0097] Example

[0098] Example 1

[0099] The dissolution of ferric fluoride trihydrate (FeF3.3H2O, abbreviated as IFH) in ethanol was tested by varying the weight of IFH and the volume of ethanol. Table 1 shows the different combinations tested and the amount of IFH dissolved, expressed as wt% based on the total weight of the solution. It is clear that the amount of IFH dissolved in ethanol increases with increasing volume of ethanol.

[0100] Table 1: Dissolution of IFH in ethanol

[0101]

[0102] Example 2

[0103] At room temperature, 1g IFH is dissolved in 15mL ethanol via stirring to obtain a yellow suspension of partially dissolved IFH in ethanol. Undissolved IFH is separated from the suspension by centrifuging the yellow suspension at 8000rpm for 5 minutes, then using syringe decantation. The limpid yellow solution is further filtered through a 0.45µm polytetrafluoroethylene (PTFE) syringe filter. Then 0.6mL distilled water (pH 6-7) is added to the solution. The white product begins to precipitate and the solution is placed in a room temperature precipitation for at least 16 hours. The precipitated product is then separated from the solution by centrifuging at 10000rpm for 5 minutes, then decantation, thus obtaining Pyr-IHFH.

[0104] The resulting Pyr-IHFH was analyzed by both scanning electron microscopy (SEM) and TEM. SEM measurements were performed using a Gemini 1530 microscope (Zeiss) operating at an accelerating voltage Uacc = 1 kV. TEM measurements were performed using a Talos F200X (ThermoFisher Scientific, FEG, Uacc = 200 kV).

[0105] Figure 2 An SEM image of the obtained Pyr-IHFH is shown, from which a spherical shape is observed. Figure 3A and 3B TEM images of the obtained Pyr-IHFH at different magnifications are shown, from which it is clearly seen that Pyr-IHFH exists as spherical particles with an average size of about 200 nm.

[0106] Then 100 mg of Pyr-IHFH was placed in a 2 mL vial in a tubular furnace (Carbolite Gero), each side of which was sealed with quartz wool. The furnace was heated to 280°C at 10°C / min and then held at 280°C for 30 minutes. The vial was then cooled at a natural cooling rate. Pyr-IHF was obtained as an orange-brown powder.

[0107] Figure 4 An SEM image of the obtained Pyr-IHF is shown, from which a spherical shape is observed. Figure 5A and 5B TEM images of the resulting Pyr-IHF at different magnifications are shown, from which it is clear that Pyr-IHF exists as spherical particles with an average size of about 200 nm. The average diameter is determined by approximating the area of ​​the particles to an ellipsoid and then calculating the diameter of the area equivalent circle.

[0108] Figure 6 The PSD of the particles is shown, which is calculated from the calculated average diameter of the particles. The PDS has the following values, which indicate a narrow PSD in the field of particulate cathode active material: d 194 nm 10 , d of 219nm 25 , d of 245nm 50 , d of 277nm 75 and 290nm d 90 .

[0109] The surface roughness of Pyr-IHFH and Pyr-IFH particles was analyzed by scanning transmission electron microscopy (STEM), especially high angle annular dark field (HAADF) STEM images. Figure 7B and 7C ) is obviously different from the surface roughness of Pyr-IHFH particles ( Figure 7A ).Depend on Figure 7C Pores inside the Pyr-IHF particles are visible.

[0110] X-ray absorption spectroscopy (XAS) spectra of both Pyr-IHFH and Pyr-IHF were recorded in transmission mode at the Fe K-edge (BM31 beamline at the European Synchrotron Radiation Facility). Spectra were acquired between 7.0 and 8.0 keV at room temperature, with a wavelength of ≈4 eV s -1 The scan was repeated 3 times and the final beam size was ≈ 6 mm × 5 mm. Figure 8A Normalized XANES areas of Pyr-IHFH 10 and Pyr-IHF 11 are shown. Figure 8B The real-space k²-weighted EXAFS spectra of Pye-IHFH 12 and Pyr-IHF 13 are shown. It is clear that Pyr-IHFH and Pyr-IHF exhibit identical curves in both the XANES and EXAFS regions, even down to the third coordination sphere at almost 7 Å, indicating that the interconnected pore structure is preserved during thermal treatment.

[0111] Example 3

[0112] The cathode was prepared using the pyrochlore iron hydroxyfluoride of Example 2. For this purpose, a slurry was prepared by adding 100 mg of Pyr-IHF (50 wt. %), 80 mg of carbon black (Super C65) (40 wt. %) as a conductive additive, and 20 mg of polyvinylidene fluoride (PVDF, 10 wt. %) to 2.4 g of N-methyl-2-pyrrolidone (NMP).

[0113] The slurry was mixed with 20 g ZrO2 balls (5 mm in diameter) in a beaker under air and ball milled at 300 rpm for 1 hour in a planetary ball mill (Fritsch, Pulverisette 7). The slurry was then scraped with a 100 μm scraper at 1 mm s- 1 The tape was cast onto carbon-coated Al foil at a rate of 100 nm to produce a uniform strip approximately 6 cm × 30 cm. The tape-cast Al foil was dried at 80°C in air until visibly dry (approximately 4 hours), then dried under vacuum at 80°C for 24 hours. Discs with a diameter of 12 mm were punched from the foil, weighed (each disc had an active material loading of 0.4-0.7 mg / cm²), and transferred to an argon-filled glove box.

[0114] Lithium-ion coin cell cells were prepared in an argon-filled glove box. Elemental lithium buttons (12 mm diameter) were used as counter and reference electrodes. A glass fiber separator was placed between the two electrodes and impregnated with 150 μL of lithium-ion conducting electrolyte. Two electrolytes were tested: a conventional carbonate electrolyte (1 M LiPF6-EC / DMC) and an ionic liquid electrolyte (in Pyr 1,4 The coin cell was then heated at 75°C for 24 hours under argon to ensure good wetting.

[0115] By comparing the + / Li in the voltage range of 2-4.2 V at room temperature at 100 mA / g AM The coin cell was electrochemically tested by galvanostatic cycling at a current rate of 1.5 GHz on a multi-channel potentiostat / galvanostat (Biologic (MPG2)).

[0116] Figure 9A and 9B Shown are respectively in Pyr 1,4 Charge and discharge voltage curves of the cells with 1 M LiPF6-EC / DMC and 1 M LiTFSI in TFSI as electrolytes after the first, second, 50th, and 200th charge / discharge cycles.

[0117] During the first discharge in EC / DMC electrolyte, 171 mA h g AM - 1 The discharge capacity of 163 mA h g in ionic liquid (IL) electrolyte is 0. AM - 1 During the first charge, approximately 30 mA h g was observed with both electrolytes. AM - 1The capacity of the second discharge process is 142mA hg in EC / DMC electrolyte. AM - 1 and 130 mA hg in 1L electrolyte AM - 1 For these reasons, the first cycle was subsequently considered as a pre-cycle and the capacity retention was calculated relative to the second cycle.

[0118] In subsequent cycles, the capacity of the cell using the EC / DMC electrolyte rapidly decreases, while the IL electrolyte shows a much higher capacity retention, indicating that the cell using the EC / DMC electrolyte has poor cycling stability. This is also reflected in the coulombic efficiency. Figure 10 The capacity and coulombic efficiency of coin cell batteries using EC / DMC electrolyte 20 and IL electrolyte 21 are shown up to 250 cycles. After 250 cycles, only 16% of the initial charge capacity of the Pyr-IHF-containing cathode measured in EC / DMC electrolyte 20 was retained. In contrast, the battery cell using IL electrolyte 21 showed an excellent Pyr-IHF cathode capacity retention of 73% after 250 cycles under the same conditions. The consistently good coulombic efficiency of 99.7% after the first cycle further demonstrates the excellent cycling stability in IL-based electrolytes such as electrolyte 21.

[0119] Figure 11 The rate performance of the coin cell using IL electrolyte is shown. AM -1 Increased to 1000mA g AM -1 When the current rate is reduced to 25mAg -1 When the capacity is mostly recovered (128 mA hg at the 10th cycle), AM -1 For the 110th cycle, 110 mA hg AM -1 ).

[0120] Example 4

[0121] Another cathode was prepared using the pyrochlore iron hydroxyfluoride of Example 2. For this purpose, a second slurry was prepared by adding 100 mg of Pyr-IHF (50 wt %), 78 mg of carbon black (Super C65) (39 wt %) and 2 mg of CNTs (1 wt %) as a conductive additive mixture to 2.4 g of N-methyl-2-pyrrolidone (NMP), as well as 20 mg of polyvinylidene fluoride (PVDF, 10 wt %).

[0122] The cathode and the battery cell were prepared with this second slurry in the same manner as detailed for the cathode in Example 3, but without any CNTs. As electrolyte only the ionic liquid electrolyte of Example 3 (in Pyr 1,4 1M LiTFSI in TFSI).

[0123] By comparing the + The coin cell was electrochemically tested by galvanostatic cycling on a multi-channel potentiostat / galvanostat (Biologic (MPG2)) at room temperature in the voltage range of 2-4.2 V for Pt / Li.

[0124] Figure 12 Shown when at 100mA / g AM The charge and discharge voltage curves of the battery with CNTs at the first, second, 20th and 100th charge / discharge cycles when tested at a current rate of Figure 9B When compared to the same cell without CNTs, it is clear that the cell with CNTs (162 mA h g- 1 ) and without CNT (163mA hg -1 ) are almost identical in the first cycle. However, the first cycle coulombic efficiency (not shown) is significantly closer to 100% (119.5% with CNTs vs. 126.2% without CNTs), indicating higher reversibility in the presence of CNTs.

[0125] Still at 1A / g AM The batteries with and without CNTs were tested with constant current at a current rate of . Figure 13A and 13B The charge and discharge voltage curves for the first, second, 100th, and 1000th charge / discharge cycles are shown. It is clear that the total capacity is significantly improved in the presence of CNTs. This suggests that electron percolation is indeed limited at high current rates and can be mitigated by the high aspect ratio of CNTs.

[0126] Figure 14 It shows that the CNTs are contained at 1A / g AM The capacity and coulombic efficiency of the battery cycled at a current rate of 1.5 GHz were measured. The coulombic efficiency remained close to 100% even after 1,000 charge and discharge cycles. In addition, the capacity retention was very high: 90.1% after 400 cycles, 86.1% after 600 cycles, and 79.1% after 800 cycles.

[0127] name

[0128] 1. Method for producing cathode active material

[0129] 2. Solution Preparation Operation

[0130] 3. Remove operation

[0131] 4. Precipitation Operation

[0132] 5. Separation operation

[0133] 6. Drying operation

[0134] 10. Pyr-IHFH

[0135] 11. Pyr-IHF

[0136] 12. Pyr-IHFH

[0137] 13. Pyr-IHF

[0138] 20. Coin Cell with EC / DMC Electrolyte

[0139] 21. Coin cell battery with ionic liquid electrolyte

Claims

1. A method for producing a cathode active material (1), comprising: - preparing (2) a solution comprising a liquid alcohol and ferric fluoride trihydrate (IFH), wherein the IFH is at least partially dissolved in a polar solvent; - precipitating (4) a compound comprising hydrated ferric hydroxyfluoride (Pyr-IHFH) by adding water to the solution; - separating the precipitated compound from the solution (5); as well as - drying (6) the separated precipitated compound to a temperature of 20-400° C., thereby obtaining the cathode active material, The method is characterized in that water is added to the solution to convert IFH into Pyr-IHFH, and the cathode material comprises pyrochlore ferric hydroxyfluoride (Pyr-IHF).

2. The method according to claim 1, wherein the ratio of the weight of IFH in the solution to the volume of the polar solvent is 0.002-0.1 g / mL.

3. The process according to any one of the preceding claims, wherein 1 to 15% by volume of water, based on the volume of the polar solvent in the solution, is added to the solution.

4. A method according to any one of the preceding claims, wherein the polar solvent is one or more of an alcohol, ethylene glycol, glycerol or an acid.

5. The process according to claim 1 , wherein the precipitated compound is dried at a temperature of 100-400° C. and atmospheric pressure.

6. The method according to any one of the preceding claims, wherein separating (5) the precipitated compound from the solution comprises one or more of centrifugation, decanting or filtration.

7. The method according to any one of the preceding claims, wherein the Pyr-IHFH comprises pores, wherein the pores have an average diameter of 2.5-5 Å as calculated by X-ray diffraction (XRD) analysis.

8. The method according to claim 7, wherein the pores are at least partially filled with water molecules.

9. A cathode active material for a cathode, comprising pyrochlore ferric hydroxyfluoride (Pyr-IHF).

10. The cathode active material according to claim 9, wherein the Pyr-IHF comprises pores, wherein the pores have an average diameter of 2.5-5 Å calculated from XRD analysis.

11. The cathode active material according to any one of claims 9-10, comprising particles comprising Pyr-IHF, wherein the particles have an average diameter of 100-500 nm as calculated by transmission electron microscopy (TEM) analysis.

12. A cathode comprising the cathode active material according to any one of claims 9 to 11.

13. The cathode according to claim 12, further comprising carbon nanotubes.

14. A battery comprising a cathode according to any one of claims 12-13.

15. The battery according to claim 14, wherein the battery is a secondary battery.

16. The battery according to any one of claims 14-15, wherein the battery is a lithium ion battery.

Images