Process for the production of fluorinated metal oxide particles

Abstract

This invention relates to a process for the production of fluorinated metal oxide particles, the fluorinated metal oxide particles obtainable with such a process, and use thereof in the preparation of a solid-state electrolyte.

Description

[0001] Title

[0002] Process for the production of fluorinated metal oxide particles DESCRIPTION

[0003] Field of the Invention

[0004] This invention relates to a process for the production of fluorinated metal oxide particles, the fluorinated metal oxide particles obtainable with such a process, and use thereof in the preparation of a solid-state electrolyte.

[0005] State of the Art

[0006] A battery, also known as pile or electrochemical cell, is an electrochemical device that converts the energy released by a chemical reaction into electricity.

[0007] A battery always consists of two electronic conductors (called electrodes) in contact with an ionic conductor, called the electrolyte. The electrodes can be liquid or solid, as in the case of lithium batteries; similarly, the electrolyte can be either solid, such as B-alumina, or liquid, as in most commercial devices.

[0008] The operation of a battery is linked to the fact that, at the separation surfaces between the electrodes and the electrolyte, the conduction of charge carriers switches from electronic to ionic, which can only happen if electrochemical reactions occur. Batteries may be classified as primary or secondary, depending on whether the electrochemical discharge reaction occurs in one direction or in both directions, respectively.

[0009] The research and industrialization of lithium batteries are due to the high electropositivity and light weight of lithium, which have facilitated the production of high-energy density systems. Primary Li batteries use lithium metal as the anode, inorganic materials such as UC0O2, MnC>2, V2O5 (intercalation compounds) as the cathode, and a solution of a lithium salt (e.g. LiCIO4) in a mixture of organic solvents (for example, ethylene carbonate and dimethyl ether) as the electrolyte, as described by Tarascon et al., Nature 4 4 (2001 ) 359-367.

[0010] To overcome the cyclability problems inherent to lithium metal (caused by passivation defects at the anode / electrolyte interface), lithium ion secondary batteries have been developed, together with the related anode and cathode intercalation materials, as reported by Thackeray et al., Material Research Bulletin 18 (1983), 461 - 472. A typical cathode intercalation material is LiCo02 (lithium cobaltate); polyoxoanionic compounds, having a structure consisting of octahedra of the MO6type with M = Fe, Ti, V, Nb and tetrahedral anions of the XC>4n' type with X = S, P, As, Mo and W, have been widely studied (Padhi et. al. Journal of the Electrochemical Society 144 (1997) 1609-1613); among these the main one is LiFePC . A typical anode intercalation material is graphite.

[0011] The purpose of electrolytes is to allow the passage of charge carriers (such as Li+) from the anode to the cathode; electrolytes must possess certain characteristics: high ionic conductivity; wide electrochemical stability window, necessary if cathode materials that are particularly oxidizing compared to Li / Li+(>4 V) are used; high thermal stability, necessary for high-temperature batteries.

[0012] Electrolytes can be divided into four main categories based on their physical state (Gray, Polymer Electrolytes, RSC Material Monographs, Cambridge, 1997):

[0013] 1 ) Liquid electrolytes: consisting, for example, of a solution of a lithium salt (e.g., LiPF6, LiBF4, or LiCIC ) dissolved in an organic solvent (e.g., ethylene carbonate) (Galinsky et al. Electrochimica Acta 51 (2006) 5567-5580). Despite their high ionic conductivity at room temperature (values between 10'2and 10'3S cm'1), liquid electrolytes have numerous disadvantages: they cause leakage and corrosion problems, they are not suitable for use at high temperatures due to their volatility and, finally, they severely limit the miniaturization of devices

[0014] 2) Solid-ceramic electrolytes', in which ionic conductivity occurs through the movement of charged point defects; they are usually used for high-temperature systems and can be classified into three categories of chemical compounds: a. perovskite-type oxides (as described by P. Knauth, Solid State Ionics, 180 (2009) 911 -916); currently, the best ceramic conductor of Li ions is based on a lanthanum titanate, where, at temperatures no higher than 127 °C, Li+is expected to move in solid solution through lanthanum vacancies; b. sulfides (Thio-LISICON-type materials, described by M. Murayama et al. Journal of Solid State Chemistry 168(1 ) (2002)140); and c. phosphates (NASICON-type materials, described by P. Knauth, op. cit.).

[0015] 3) Solid-glassy electrolytes: these are amorphous solids obtained by cooling liquids; at room temperature, ionic conductivity values range between 10'2and 10'5S cm'1.

[0016] 4) Molted electrolytes: consisting of eutectic mixtures of molten salts, they are used in high-temperature Li batteries, such as the LiCI / KCI mixture, whose eutectic point is 355°C. The main disadvantage lies in the need to maintain the device at a high temperature and the use of very aggressive reagents.

[0017] These first four categories of electrolytes share a common disadvantage: they require liquid electrodes, such as molten metals (sodium) or molten salts (NaSx) to ensure constant contact between the electrodes and the electrolyte.

[0018] Polymer electrolytes appear to be possible candidates for the production of entirely solid-state devices. This family includes several subsets of materials: a. Gel electrolytes, in which the lithium salt is dissolved in a polar liquid to which an inert polymer material is subsequently added for greater stability; b. Plasticized electrolytes, in which a liquid with a high dielectric constant is added to a polymer electrolyte to improve its ionic conductivity; c. “Ionic rubbers” which are obtained by adding a high-molecular-weight polymer to a liquid electrolyte; d. Ionic conducting membranes, similar to those used in fuel cells; e. Organic-inorganic hybrid electrolytes, whose basic structure consists of a series of organic macromolecules (for example, polyethylene oxide, PEO) that act as bridges between inorganic species. Examples of organic-inorganic hybrids are 3D- HION-APEs (three-dimensional hybrid inorganic-organic network sas polymer electrolytes), Z-IOPEs (zeolite inorganic-organic polymer electrolytes), and HGE (hybrid gel electrolytes).

[0019] In addition to lithium ion batteries, secondary batteries using ions other than Li, such as Na, K, Ca, Mg, and Al, are known, at least in the research and development phase.

[0020] Sodium ion batteries (SIBs) and potassium ion batteries (KIBs) are batteries that use sodium (Na+) or potassium (K+) ions as charge carriers. In some cases, the cell operating principle and construction are similar to those of lithium ion (Li+) batteries but Li+is replaced with Na+or K+as intercalating ions. Na and K belong to the same group as Li in the periodic table and therefore have similar chemical properties. In particular, SIBs have received greater academic and commercial interest due to the high cost of lithium, its uneven geographic distribution, and its environmentally harmful extraction process. An obvious advantage of sodium is its natural abundance, particularly in saltwater. Another factor is that cobalt, copper, and nickel used in LIB cathodes are not required for many types of sodium ion batteries, and more abundant iron-based materials (such as NaFeO2with the Fe37Fe4+redox couple) work well in SIBs. SIBs use “hard carbon”, a disordered carbon-based material consisting of non-graphitizable, non-crystalline, and amorphous carbon, as anodes. Low-cost iron and manganese oxides can be used as cathodes in SIBs, while lithium ion batteries require the use of more expensive cobalt and nickel oxides. The disadvantage of the larger size of the Na+ion is its slower intercalation kinetics compared to the Li+ion, and the presence of multiple intercalation stages with different charge / discharge potentials and kinetics. Polar aprotic solvents of alkyl carbonate esters, including ethylene carbonate, dimethyl carbonate, and diethyl carbonate, are widely used as electrolytes in SIBs. The most commonly used salts are NaCIC and sodium hexafluorophosphate (NaPF6) dissolved in a mixture of these solvents (Hwang, Chem. Soc. Rev. 46 (2017) 3529). Among the solid electrolytes for SIBs, inorganic ones (for example, Na-(3-AI2O3, NASICON and NasPS^, solid polymeric ones based on PEO, PVDF-HFP, and PAN, and solid crystalline plastic ones mainly composed of succinonitrile (Zhao et al. Electrochem. Energy Rev. 2024, 7:3) can be mentioned. Together with the sodium ion, the potassium ion is the main candidate for chemical replacement of lithium ion batteries, hence the KIB batteries. The anode can be based on graphite or other carbonaceous materials, the cathode is based on Prussian White derivatives or potassium transition metal oxides with a layered structure such as K0.3MnO2, K0.55CoO2(Pramudita J.C. et al. Adv. Energy Mater. 7(2017) 1602911 ). Solid-state electrolytes for KIBs (sulfides, oxides and phosphidosilicates) show promising bulk electrochemical (low activation energy and ionic conductivity at relatively high room temperature) and interfacial (stable cycling up to 1000 cycles) performances (Grill, J. et al. Commun Mater 5 (2024), 127).

[0021] In addition to the lithium ion battery technology, rechargeable multivalent lithium ion batteries, such as magnesium, calcium, and aluminium ion batteries, have attracted increasing research efforts in recent years. With a reduction potential of -2.37V (compared to the standard hydrogen electrode, which is close to that of Li, -3.045V) and a lower tendency to form dendrites, Mg anodes can potentially deliver high energy with stable performances. Compared to lithium ion batteries, magnesium ion batteries (MIBs) also benefit from higher material abundance, improved safety, and lower cost (Leong K.W. et al. Sci. Adv. 9 (2023), eadh 1181 ). Magnesium intermetallic compounds (e.g., Mg3Bi2and, in addition to bismuth, tin and antimony have been used in composite insertion electrodes) are used as anode materials due to their lower reactivity with common electrolytes, making them less prone to passivation. Materials based on zirconium disulfide, cobalt (II, III) oxide, tungsten diselenide, vanadium pentoxide, and vanadates are being studied as cathodes. Electrolytes are very diverse: Grignard reagents, magnesium organoboranes (e.g., Mg(BPh2Bu2)2 used for the first time for secondary batteries), and magnesium borohydrides (e.g. Mg(BH4)(NH2) as an example of a solid-state electrolyte).

[0022] Calcium ion batteries (CIBs) are rapidly emerging as an alternative to the Li-ion technology due to their similar performance, the greater abundance of Ca compared to Li, and lower costs. Calcium anodes have focused on the use of metal anodes, metal oxides, carbons, and metal / semiconductor as alloys compounds. Examples include vanadium oxide (V2O5), copper-calcium alloys, Mg-V2O5 / graphite, calcium metal, and silicon anodes (Tinker H.R. et al. Mater. Adv., 4(2023) 2028). CIB electrolytes exhibit low electrochemical stability; however, the use of Ca(CIO4)2 and Ca(BF4)2salts in organic solvents avoids unwanted passivation reactions of the (anodic) calcium metal. Solvents such as water and alkyl carbonates, ionic liquids, mixed cationic electrolytes with Li / Ca and Na / Ca (BH4and PF6' anions) and K / Ca (PF6‘ anion) have been investigated. Calcium salts explored in liquid electrolytes include calcium tetrafluoroborate (Ca(BF4)2, calcium borohydride (Ca(BH4)2, calcium bis(trifluoromethanesulfonimide) (Ca(TFSI)2), calcium perchlorate (Ca(CIO4)2), calcium hexafluorophosphate (Ca(PF6)2) and calcium nitrate (Ca(NO3)2), although the latter is commonly used in aqueous solvent CIB batteries. As cathodes, calcium metal oxides and sulfides are areas of study; candidates include calcium / manganese mixed oxide, calcium / cobalt mixed oxide, titanium disulfide, and Prussian blue derivatives (Wu Y. Et al. Carbon Neutralization 2 (2023) 551 ).

[0023] Aluminium ion batteries (AIBs) are a class of rechargeable batteries in which aluminium ions act as charge carriers. Aluminium can exchange three electrons per ion, meaning that the insertion of one Al3+is equivalent to inserting three Li+ions. Because the ionic radii of Al3+(0.54 A) and Li+(0.76 A) are similar, a greater number of electrons and Al3+ions can be accepted by the cathodes (greatly increasing the capacity of the AIB). Metallic aluminium and its alloys are widely used as anodes. Currently, the most commonly used electrolyte for rechargeable AIBs are nonaqueous ionic liquids that are acidic at room temperature and consist of adducts of aluminium chloride (AICI3) and 1 -ethyl-3-methylimidazole chloride ([Emlm]CI). Cathode materials currently used in AIBs can be divided into three main categories: carbon-based materials, transition metal compounds, and organic materials. Organic materials have significantly different structures than inorganic ones, and therefore their preparation and modification methods are also distinct (Yang X. Journal of Energy Storage, 78 (2024) 110069).

[0024] The International Patent Application No. WO 2012 / 017347 describes a process for the production of fluorine-doped TiO2involving multiple hydrothermal steps through a wet route. The International Patent Application No. WO 2013 / 011423 describes the use of particles of at least one, preferably metallic, crystalline oxide with a particle size of less than 500 nm and a fluorine content of between 0.5 and 30% by weight, preferably between 0.5 and 5%, and even more preferably between 1 .0 and 4%, in the preparation of solid-state electrolytes.

[0025] A solid state electrolyte is also described, consisting of particles of at least one, preferably metallic, crystalline oxide having an average particle size of less than 500 nm, preferably between 10 and 500 nm, even more preferably between 50 and 300 nm; a fluorine content of between 0.5 and 30% by weight, preferably between 0.5 and 5%, even more preferably between 1 and 4%; an alkali metal or alkaline earth metal content of between 0.5 and 10% by weight, preferably between 0.5 and 5%, even more preferably between 1 and 4%.

[0026] An inorganic-organic hybrid electrolyte, obtainable by reacting the aforementioned solid-state electrolyte with ionic liquids, is also described.

[0027] The International Patent Application No. WO 2022 / 269462 describes a process for the production of fluorinated metal oxide particles in which the fluorinated metal oxides are subjected to hydrothermal treatment in a steam atmosphere at a relative pressure of between 0.01 bar and 10 bar and a temperature of between 350°C and 500°C, preferably for a period of between 0.5 and 24 hours.

[0028] Summary of the Invention

[0029] An object of the present invention is to provide a new process for the production of fluorinated metal oxide particles that is more advantageous than the one described in the International Patent Application No. WO 2012 / 017347, in terms of simplified steps, as well as lower reaction time and temperature.

[0030] The use of mechanochemical synthesis techniques according to the present invention allows to produce fluorinated oxides in a one-step process, rather than the multi-step process described in the International Patent Application No. WO 2012 / 017347, with significant process simplifications.

[0031] Advantageously, the process according to the present invention requires a significantly simplified plant, allows for better control of the process stoichiometry and therefore of the final products, while achieving the same conductivity of the final electrolytes (post-lithiation).

[0032] Therefore, the present invention relates, in a first aspect thereof, to a process for the production of fluorinated metal oxide particles according to claim 1 .

[0033] According to a second aspect thereof, the present invention relates to fluorinated metal oxide particles obtainable according to the process of the invention.

[0034] According to a third aspect thereof, the present invention relates to the use of the aforementioned fluorinated metal oxide particles for the preparation of a solid-state electrolyte.

[0035] Description of the Figures

[0036] Figure 1. EDS spectrum of F- and N-doped titanium oxide powders prepared according to Example 1 .

[0037] Figure 2. IR spectrum of commercial NH4F and TiC>2 reagents and post-grinding TiF powders.

[0038] Figure 3. EDS spectrum of F- and N-doped titanium oxide powders prepared according to Example 2.

[0039] Figure 4. Electrochemical impedance spectrum of the solid-state electrolyte for Na ions (“NaFT”) described in Example 4.

[0040] Definitions

[0041] Unless otherwise defined, all terms of the art, notations and other scientific terminology used herein are intended to have the meanings commonly understood by those skilled in the art to which this disclosure pertains. In some cases, terms with commonly understood meanings are defined herein for clarity and / or for ready reference; thus, the inclusion of such definitions in the present disclosure should not be construed to represent a substantial difference over what is generally understood in the art.

[0042] The terms “approximately” and “about” used in the text refer to the range of the experimental error that is inherent in the execution of an experimental measurement.

[0043] The terms “comprising”, “having”, “including” and “containing” are to be intended as open-ended terms ( / .e., meaning “comprising, but not limited to”), and are to be considered as a support also for terms such as “consist essentially of”, “consisting essentially of”, “consist of”, or “consisting of”.

[0044] The terms “consist essentially of”, “consisting essentially of” are to be intended as semi-closed terms, meaning that no other ingredients affecting the novel features of the invention are included (optional excipients may therefore be included).

[0045] The terms “consists of”, “consisting of” are to be intended as closed terms.

[0046] The term “room temperature” refers to a temperature of between 15°C and 25°C, preferably between 20°C and 25°C.

[0047] The term “rotational speed” refers to the number of complete revolutions of a point along a circumference per unit of time. In rotary mills, the rotational speed is that of the grinding jar, and the number of revolutions is measured as the number of revolutions per minute (rpm). In planetary mills, the rotational speed is that of the rotating support (typically a disk) on which the vials are arranged, as well as that of the vials around their own axis.

[0048] The term “frequency” refers to the number of oscillations per unit of time, measured in hertz (number of vibrations per second). In vibratory mills, frequency is the quantity that describes the vibration intensity of the container (typically a jar) containing the sample and the grinding bodies (typically balls) that oscillate left and right along a straight or slightly curved trajectory.

[0049] The terms “mechanosynthesis’’ or “mechanochemical synthesis” refer to the branch of chemistry that studies the effects of impact and friction forces (typically generated in grinding media) to initiate chemical syntheses, typically through the use of ball mills or other mechanical systems. The mechanical energy of impacts (mechanical collisions) between the grinding media is converted into thermal energy, which can be locally / point-specifically high enough to induce chemical reactions.

[0050] Detailed Description of the Invention

[0051] More specifically, the present invention relates to a mechanochemical process for the production of fluorinated metal oxide particles by mechanosynthesis, characterized in that it comprises a mixing step between a mixture of at least one metal oxide or inorganic electrolyte and at least one fluorinating agent; said mixing step is performed in a hard material grinding system (mill) comprising a closed container and grinding media, preferably made of one or more of the following hard materials: steel, agate, zirconia, tungsten carbide, silicon carbide, and silicon nitride.

[0052] Preferably, said grinding media are grinding bodies, more preferably grinding balls.

[0053] In mechanosynthesis, the choice of an appropriate material for the grinding container / reactor, typically a jar, and the grinding bodies, typically balls, is crucial. In most cases, the materials of the grinding jar and balls are different from those of the powder being processed. Consequently, the ground material will likely be contaminated to some extent by abrasion from the grinding device, known as the mill. The extent of abrasion depends on several factors, including the hardness of the ground powder, the wear resistance of the mill engineering materials, the ball-to- powder weight ratio, and the grinding power. Common materials used for making the vessel / reactor and grinding bodies include various types of steel (for example, hardened steel, stainless steel) and tungsten carbide, engineering ceramics such as sintered corundum, yttria-stabilized zirconia, agate, and silicon nitride (Si3N4).

[0054] It was found that frictional heating, achieved by the intense agitation generated by suitable mills, results in the decomposition of fluorinated compounds, in gaseous HF and ammonia, inter alia, which react with the reactive surface of the oxide substrate. The result is the functionalization / doping of the oxide surface without resorting to multi-step hydrothermal processes through a wet route, as described in the International Patent Application No. WO 2012 / 017347.

[0055] Advantageously, the oxide produced mechanochemically according to the present invention can undergo the same traditional drying and lithium (or sodium) functionalization treatments to produce solid-state electrolytes for lithium (or sodium) secondary batteries.

[0056] The main types of commercial mills that can be used for the purposes of the present invention are rotary mills, vibratory mills, and planetary mills.

[0057] In rotary mills, the grinding vessel / container (also known as a grinding jar) is loaded with the grinding media (preferably balls) and reagents in the required amount. This operation is preferably carried out in a protective atmosphere (for example, of argon in a glove box, controlled atmosphere) when using reactive reagents, to prevent their oxidation and contamination. Process control additives are optionally added to the grinding mixture, primarily to minimize particle agglomeration by acting as lubricants and surfactants. The grinding jar is then sealed and secured inside the mill, where grinding takes place for the desired time at an appropriate frequency (revolutions per minute, or rpm). Finally, the ground material is recovered, and contaminants from the ground materials can optionally be removed as a final step.

[0058] In rotary mills, the quantity describing the intensity of rotation is the rotational speed of the jar, measured in rpm.

[0059] In a preferred embodiment, the rotational speed ranges from 100 to 3,000 rpm, preferably from 500 to 2,000 rpm, and more preferably from 600 to 1 ,000 rpm.

[0060] In vibratory mills, the jar containing the sample and the grinding balls oscillates left and right along a straight or slightly curved path.

[0061] In vibratory mills, the quantity that describes the intensity of vibration is frequency, defined as the number of oscillations per unit of time, measured in hertz (number of vibrations / second).

[0062] In a preferred embodiment, the frequency ranges from 10 Hz to 100 Hz, preferably from 25 Hz to 35 Hz.

[0063] In planetary mills, the vials are arranged on a rotating support (typically a disk), where a drive mechanism also causes them to simultaneously rotate around their axes. As the vials and the supporting disk rotate in opposite directions, centrifugal forces act alternately in equal and opposite directions. This allows the balls to slide along the inner wall of the vial (exerting friction) and then suddenly project and collide with the opposite side (exerting a strong impact). Thus, impacts (collisions) and shear stresses among the balls contribute to the overall mechanical stress exerted on the material.

[0064] In planetary mills, therefore, two quantities are involved: the rotational speed of the rotating support, whose rotational speed is generally measured in rpm; the rotational speed of the vials around their own axis in the opposite direction, whose rotational speed is generally indicated by the ratio “k” between the speed of the vials (cov) and the rotational speed of the rotating support (cod), where k = -cov / cod.

[0065] In a preferred embodiment, the rotational speed of the rotating support ranges from 50 to 1000 rpm, preferably from 400 to 700 rpm; and the “k” ratio ranges from -1 to - 5, preferably from -2 to -3.

[0066] In planetary systems, therefore, combinations of friction, shear, and impacts are generated, unlike in vibrating mills, where the impacts (collisions) of the balls are dominant.

[0067] Preferably, the metal oxide is selected from titanium, iron, copper, silicon, zinc, tungsten, and tantalum oxides.

[0068] As an alternative to the metal oxide, an inorganic electrolyte selected from the following classes may be used:

[0069] - solid ceramic electrolytes of the lithium oxide type, typically this means perovskite structures such as LLTO, whose composition is Li3xLa2 / 3-xTiO3 with 0.03 < x < 0.17;

[0070] - lithium sulfides (Li6PS5X with X = Cl, Br, I, or Li10GeP2Si2);

[0071] - NaSICON (sodium super ionic conductor): LAGP (Lii+xAlxGe2-x(PO4)3 or LATP (Li1+xAlxTi2-x(PO4)3) with 0.1 < x < 0.6;

[0072] - garnet (Li7La3Zr20i2, LLZO).

[0073] In a preferred embodiment of the process according to the invention, the fluorinating agent is selected from ammonium fluorides, ammonium fluorometallates, alkali and alkaline earth metal fluorides, or mixtures thereof, preferably NH4HF2, NH4F, (NH4)2TiF6, (NH4)3FeF6, (NH4)2SiF6, Li F, NaF, or mixtures thereof.

[0074] In a preferred embodiment of the process according to the invention, the mixing step is carried out at a temperature of between -100°C and +300°C, preferably between 50°C and 200°C.

[0075] For this purpose, there are mills allowing for continuous temperature monitoring throughout the entire grinding process by means of cooling and heating, thus ensuring flexible and safe temperature regulation.

[0076] In some technological solutions, sample cooling and heating can be achieved using “thermal plates”; when the grinding jars come into contact with the thermal plates, heat is effectively transferred to or from the jars through electromagnetic induction.

[0077] Other technological solutions involve the use of thermal fluids (for example, liquid nitrogen).

[0078] In this latter configuration, the vibratory mills may be connected to a cryostat, a refrigerator, or a tap. The external temperature control adjusts the corresponding thermal fluid to a defined temperature, and this thermal fluid transfers this temperature to the thermal plates. Since significant heat can also be generated inside the jar during the grinding process, the temperature of the thermal plates can be monitored and adjusted.

[0079] The effective temperature of the thermal plates depends on both the thermal fluid temperature and the grinding parameters, such as frequency, time, jar volume, and grinding ball size.

[0080] The mixing step is preferably carried out for a period of between 10 minutes and 24 hours, preferably between 1 and 10 hours.

[0081] The grinding time is the total duration of grinding. The initial time is the time when the grinding operation begins, the final time is the time when grinding ends (the initial sample thermostating time, i.e., heating or cooling the jar to the setpoint temperature, is not considered, nor is the time required to bring the jar back to handling conditions). If the entire process consists of multiple consecutive grinding steps (necessary, for example, to extract and analyze sample aliquots), the (total) grinding time is the sum of all the partial times during which grinding is active.

[0082] In a preferred embodiment of the process according to the invention, the mixing step is carried out in an atmosphere of ambient air or in an atmosphere of at least one inert gas, preferably He, Ar, Kr, Xe, N2, CO2, CO, or mixtures thereof, or in an atmosphere of at least one reducing gas, preferably H2.

[0083] An important parameter for carrying out mechanosynthesis reactions is the composition of the (initial) atmosphere inside the jar. The composition of the atmosphere in the jar can change due to gases that may be generated during grinding.

[0084] Reactions can be carried out in ambient air (with the presence of oxidizing oxygen) if the reagents are not subject to oxidation (e.g., metal oxides) or if explosive reactions are not possible (due to instability and flammability of at least one reagent). If there is a risk of explosive reactions or if easily oxidizable reagents are used (e.g., carbon or metal substrates), it is necessary to work in an inert atmosphere using argon or other inert gases.

[0085] If the mechanosynthesis reaction involves a chemical reduction, the jar can be purged with reducing gases such as CO or hydrogen.

[0086] In a further preferred embodiment of the process according to the invention, said mixing step is followed by a heat treatment and / or washing step.

[0087] Preferably, the heat treatment step is carried out in a temperature range of 50°C to 2,000°C, preferably from 100°C to 800°C.

[0088] More preferably, said heat treatment step is carried out for a period of 1 to 48 hours, preferably 2 to 12 hours. In a preferred embodiment of the process according to the invention, said heat treatment step is carried out in an atmosphere of ambient air, or in an atmosphere of at least one inert or reducing gas.

[0089] Preferably, said at least one inert gas is selected from He, Ar, Kr, Xe, N2, CO2, CO, or mixtures thereof.

[0090] Preferably, said at least one reducing gas is H2.

[0091] In a further preferred embodiment of the process according to the invention, said washing step is carried out by mixing the fluorinated metal oxide with a solvent selected from water, alcohols, ketones, ethers, or mixtures thereof, preferably water, ethanol, isopropanol, acetone, dimethyl ether, diethyl ether, or mixtures thereof.

[0092] Following the mechanosynthesis reaction, the resulting powder may require some post-treatments to increase its purity or refine its crystalline structure / chemical composition.

[0093] As regards to purity, appropriate precautions must be taken to compensate for or eliminate additional elements (pollutants) incorporated into the final powder if the jar and balls materials are different from the reactants. Generally, the nominal designation of the jar material is not sufficient; the exact formulation is crucial. For example, steel, along with iron (already active in numerous catalytic activities), could contain many other metals (e.g., Ti, Cr, Mn, Ni, Cu, and Mo) that are likely found in the final powders. Tungsten carbide jars may contain varying amounts of Co or Ni as binders. Corundum-based ceramics or stabilized zirconium ceramics will possibly include a combination of different metal oxide phases in small amounts to promote sintering, as with those based on Si3N4. Therefore, washing with various solvents (aqueous / hydroalcoholic or nonpolar) is necessary.

[0094] As regards to refinement of the final powder structure, high-temperature heat treatments (if necessary, carried out in a controlled atmosphere) can both ceramize, that is, stabilize, the structure obtained from mechanosynthesis, and modify the crystalline composition (generally, heating followed by gentle cooling increases the crystallinity of inorganic solids).

[0095] The present invention also relates to the fluorinated metal oxide particles obtainable according to the process of the invention.

[0096] Furthermore, the present invention relates to the use of the aforementioned fluorinated metal oxide particles for the preparation of a solid-state electrolyte.

[0097] The solid-state electrolytes prepared using the fluorinated metal oxide particles of the invention can then be used in batteries, preferably in high-temperature lithium secondary batteries, sodium batteries or magnesium batteries.

[0098] The following examples are intended to further illustrate the invention without limiting it.

[0099] EXAMPLE 1

[0100] Production of titanium oxide with 10% fluorine by weight

[0101] 12 g of commercial titanium dioxide, 3 g of NH4F, and the appropriate quantity of grinding balls are poured into a jar of hard material (for example, zirconia or agate). The jar is placed in a machine called ball mill, and rotated at a rotational speed of 600 rpm for a time sufficient to heat the jar as a result of intense mixing, preferably to a temperature of at least 70°C. This heat promotes the thermal decomposition of the fluorinating agent into NH3and HF, which react with the titanium dioxide particles. The SEM-EDS analysis of a sample aliquot is shown in Fig. 1.

[0102] Quantification reveals that the weight fractions of F and N are 11.1 and 1.6% by weight, respectively. Infrared spectroscopy (IR) investigation shows (see Fig. 2) that the post-grinding product is similar to the F- and N-doped titanium dioxide powder obtained by hydrothermal processing (as described in the International Patent Application No. WO 2012 / 017347).

[0103] The IR spectrum of TiF shows new absorption peaks compared to the original commercial titanium dioxide: the peak at 1423 cm'1and the band of 2400-3400 cm'1are caused by N-H bond vibrations.

[0104] The final spectrum of the TiF product does not show the IR absorption peaks typical of the NH4F reagent, which means that the mechanochemical reactions of decomposition of the salt itself and functionalization of the Ti oxide have occurred, and based on the current state of our knowledge, this is analogous to the “traditional” hydrothermal process.

[0105] EXAMPLE 2

[0106] Production of titanium oxide with 20% nominal fluorine by weight

[0107] 12 g of commercial titanium dioxide, 6.2 g of NH4F, and the appropriate quantity of grinding balls are poured into a jar of hard material (for example, zirconia or agate). The jar is placed in a machine called ball mill and rotated at a rotational speed of 600 rpm for more than 2 hours. At the end of the test, the jar is hot, as a result of the intense stirring. This heat promotes the thermal decomposition of the fluorinating agent into NH3and HF, which react with the titanium dioxide particles. SEM-EDS analysis of a sample aliquot (Fig. 3) shows that the F content is equal to 16.9% by weight.

[0108] EXAMPLE 3

[0109] Preparation of a solid-state electrolyte for lithium ions pressure of 10'1mbar for 24 hours, is treated with a solution of n-butyllithium in hexane for the time needed to complete the reaction at room temperature, in a glove box with argon (residual oxygen and H2O <0.1 ppm). Once the lithiation reaction is complete, the purple solid is washed three times with anhydrous hexane. After final drying, the solid is pulverized by hand, and the resulting powder is used to prepare a pellet of 13 mm in size and approximately 100 pm thick. The pellet is placed between two blocking electrodes and, using electrochemical impedance spectroscopy, the ionic conductivity is measured and results to be approximately 10'5 / 10'4S cm'1at room temperature; this value is in line with the state of the art for solid-state electrolytes for lithium batteries.

[0110] EXAMPLE 4

[0111] Production of a solid-state electrolyte for sodium ions

[0112] 200 mg of oxide obtained according to Example 1 , after drying at 70°C under a pressure of 10'1mbar for 24 hours, is reacted with molten sodium at 98°C for the time needed for the reaction to be completed, in a glove box with argon (residual oxygen and H2O <0.1 ppm). Once the sodiation reaction is complete, the solid is washed three times with dry ethanol. Once the final drying process to remove all the ethanol is completed, the resulting solid (named “NaFT”) is pulverized by hand and, with the resulting powder, a pellet measuring 13 mm in size and approximately 100 pm thick is prepared. The pellet is placed between two blocking electrodes and, using electrochemical impedance spectroscopy, the ionic conductivity is measured and results to be approximately 10'4S cm'1at room temperature. Fig. 4 shows a graphical representation of the real component of the ionic conductivity (in S cm'1) vs. frequency (in Hz) of the alternating electric field: the intercept with the y-axis is the ionic conductivity value. The NaFT produced by sodiation of fluorinated titanium oxide obtained by mechanosynthesis according to the present invention has a slightly higher ionic conductivity than the fluorinated Ti oxide obtained by the hydrothermal process described in the International Patent Application No. WO 2012 / 017347, thus demonstrating the advantage of using the process according to the present invention.

Claims

CLAIMS1 . A process for the production of fluorinated metal oxide particles characterized in that it comprises a mixing step between a mixture of at least one metal oxide or inorganic electrolyte and at least one fluorinating agent, said mixing step being carried out in a grinding system of hard material comprising a closed container and grinding media.

2. Process according to claim 1 , characterized in that the hard material constituting the container is selected from steel, agate, zirconia, tungsten carbide, silicon carbide, and silicon nitride.

3. Process according to claim 1 or 2, characterized in that the hard material constituting the grinding media is selected from steel, agate, zirconia, tungsten carbide, silicon carbide, and silicon nitride.

4. Process according to any one of the preceding claims, characterized in that said grinding system is selected from rotary mills, vibrating mills, and planetary mills.

5. Process according to claim 4, characterized in that said grinding system is a rotary mill and said mixing step is performed at a rotational speed of 100 to 3000 rpm, preferably 500 to 2000 rpm, more preferably 600 to 1000 rpm.

6. Process according to claim 4, characterized in that said milling system is a vibrating mill, and said mixing step is performed at a frequency of 10 Hz to 100 Hz, preferably 25 Hz to 35 Hz.

7. Process according to claim 4, characterized in that said grinding system is a planetary mill comprising one or more vials arranged on a rotating support, and said mixing step is performed at a rotating support rotational speed of 50 to 1000 rpm, preferably 400 to 700 rpm, wherein the ratio k between the rotational speed of the one or more vials (cov) and the rotational speed of the rotating support (cod) rangesfrom -1 to -5, preferably -2 to -3.

8. Process according to any one of the preceding claims, characterized in that said grinding media are grinding bodies, preferably grinding balls.

9. Process according to any one of claims 1 to 8, characterized in that said metal oxide is selected from titanium oxide, iron oxide, copper oxide, silicon oxide, zinc oxide, tungsten oxide, and tantalum oxide.

10. Process according to any one of claims 1 to 8, characterized in that said inorganic electrolyte is selected from perovskite, lithium sulfides, NaSICON and garnet; preferably selected from Li3xLa2 / 3-xTiO3with 0.03 < x < 0.17, LiePSsX with X = Cl, Br, I, Li10GeP2Si2, Li1+xAlxGe2-x(PO4)3or Li1+xAlxTi2-x(PO4)3 with 0.1 < x < 0.6 and Li7La3Zr20i2.1 1. Process according to any one of the preceding claims, characterized in that said at least one fluorinating agent is selected from ammonium fluorides, ammonium fluorometallates, alkali and alkaline earth metal fluorides, or mixtures thereof, preferably NH4HF2, NH4F, (NH4)2TiF6, (NH4)3FeF6, (NH4)2SiF6, LiF, NaF, or mixtures thereof.

12. Process according to any one of the preceding claims, characterized in that said mixing step is carried out at a temperature of between -100°C and +300°C, preferably between 50°C and 200°C.

13. Process according to claim 12, characterized in that said temperature is controlled by a thermoregulation system.

14. Process according to any one of the preceding claims, characterized in that said mixing step is carried out for a time of between 10 min and 24 hours, preferably between 1 and 10 hours.

15. Process according to any one of the preceding claims, characterized in thatsaid mixing step is carried out in an atmosphere of ambient air or in an atmosphere of at least one inert gas, preferably He, Ar, Kr, Xe, N2, CO2, CO or mixtures thereof, or in an atmosphere of at least one reducing gas, preferably H2.

16. Process according to any one of the preceding claims, characterized in that said mixing step is followed by a heat treatment and / or washing step.

17. Process according to claim 16, characterized in that said heat treatment step is carried out in a temperature range of 50°C to 2000°C, preferably 100°C and 800°C.

18. Process according to claim 16 or 17, characterized in that said heat treatment step is carried out for a time of 1 hour to 48 hours, preferably 2 to 12 hours.

19. Process according to any one of claims 16 to 18, characterized in that said heat treatment step is carried out in an atmosphere of ambient air or in an atmosphere of at least one inert or reducing gas.

20. Process according to claim 16, characterized in that said washing step is carried out by mixing the fluorinated metal oxide with a solvent selected from water, alcohols, ketones, ethers or mixtures thereof, preferably water, ethanol, isopropanol, acetone, dimethyl ether, diethyl ether, or mixtures thereof.

21. Fluorinated metal oxide particles obtainable according to the process of any one of claims 1 to 20.

22. Uso of fluorinated metal oxide particles according to claim 21 , for the preparation of solid-state electrolytes.

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