Method for obtaining precursors of mixed oxides

Abstract

The present invention belongs to the field of materials production, and more specifically to a method for producing precursors of mixed oxides using a synthetic route that begins with organic acid salts and other organic compounds, based on a step of mixing using a high-shear mixer and a subsequent heat treatment, to thus produce mixed oxides, which can be used, for example, as cathode material for batteries. This synthetic route is simple and fast, has low energy use, is environmentally friendly, and neither the starting materials nor the resulting by-products are harmful to health. Furthermore, at an industrial level, it is easily scalable.

Description

[0001] DESCRIPTION

[0002] METHOD FOR OBTAINING MIXED OXIDE PRECURSORS

[0003] The present invention pertains to the field of materials manufacturing, and more specifically, to a method for manufacturing mixed oxide precursors via a synthetic route starting from salts of organic acids and other organic compounds. This method is based on a mixing stage performed using a high-shear mixer, followed by heat treatment, to produce mixed oxides useful, for example, as cathode material for batteries. This synthetic route is simple, fast, energy-efficient, and environmentally friendly, and both its starting materials and resulting byproducts are harmless to health. Furthermore, it is easily scalable at an industrial level.

[0004] BACKGROUND OF THE INVENTION

[0005] Climate change and the growing scarcity of fossil fuels are forcing modern society to evolve towards renewable and more sustainable energy sources. However, most renewable sources are intermittent, making it necessary to find systems that store the energy produced and release it on demand.

[0006] Similarly, if we want to achieve a low-carbon economy that is less dependent on fossil fuels, we need to achieve full electrification of vehicles. In this context, rechargeable batteries such as lithium-ion batteries (LIBs) or sodium-ion batteries (SIBs) play a crucial role [S. Afroze et al., Recycling (2023), 8(39), 48; Q. Li et al. Green Energy & Environment (2016), 1 (1)].

[0007] Liquid-in-body batteries (LIBs) have revolutionized portable devices, and their use in electric vehicles is growing. Sodium-in-body batteries (SIBs) are a cheap alternative to LIBs due to the abundance of sodium, making them an excellent option for large-scale energy storage. However, in both cases, cathode behavior is the main obstacle to achieving higher energy density, due to the structural changes they undergo during charging and discharging, among other detrimental processes [L. Xiao et al., Nano Energy (2015), 16, 143-151; P. Lu et al., Chem Mater. (2015), 27(4), 1381-1390]; J. Zheng et al., Chem. Mater. (2015), 27(4), 1381-1390]. Therefore, to achieve batteries with higher energy density, longer runtime, and greater safety, new cathode materials are needed.

[0008] Although there are a number of candidate materials for use as cathodes in LIBs or SIBs that, theoretically, allow significant improvements or offer other advantages, their development is still subject to improvement [Y. Liu et al., Science 2021, 24(4), 102332; Y. Yang et al., Advances in Applied Energy 2023, 11, 100146].

[0009] Furthermore, this improvement in new cathode materials must be coupled with the development of new, more efficient and environmentally friendly synthetic routes.

[0010] Commercial cathodes for lithium-ion batteries are mostly manufactured by solid-state reaction of mechanically alloyed oxides (see, for example, KB Hatzell et al., MRS Energy and Sustainability 2021, 8(1), 22-29). This process is called mechanochemistry or mechanosynthesis and is defined as the chemical reaction induced by the absorption of mechanical energy. This mechanical energy activates surfaces and generates lattice defects in the powders, surface radicals, and even bond breaks, leading to the activation and chemical reaction of the mixed powders. In the most common case of manufacturing by solid-state mechanical alloying, mixing times are at least several hours (see, for example, Q. Jiang et al., RSC Adv. 2015, 5(92), 75145-75148), making this technique inefficient and costly.Furthermore, the amount of mixture is limited by the typical volumes of the grinding vessels, which range from 50 ml to 500 ml. Similarly, the mills generally used (planetary model) have a high cost, exceeding €6,000.

[0011] Apart from solid-state reaction techniques, other methods commonly used for manufacturing cathodes for LIBs or SIBs involve coprecipitation mechanisms (see, for example, [J. Langdon et al., Energy Storage Materials 2021, 37, 143-160]). These techniques rely on controlling the nucleation and growth kinetics of particles within a supersaturated solution, where factors such as temperature, pressure, concentration, pH, mixing speed, reaction times, and the nature of the precursors play a crucial role in particle size, shape, and dispersion. Coprecipitation techniques typically involve mixing times of 1 to 2 hours and at least 10 hours of heating to evaporate all the solvent [J. Langdon et al., Energy Storage Materials 2021, 37, 143-160].

[0012] Any of the synthesis methods described above require long times for the synthesis of mixed oxides suitable for catalysts and, in addition, the volume of material that can be obtained from them is restricted, since they require a costly and highly complex infrastructure to carry them out, which in turn is an obstacle to the large-scale production of such mixed oxides for catalysts.

[0013] In order to overcome the limitations of the materials and methods for manufacturing cathodes in the state of the art, an alternative method suitable for manufacturing battery cathodes is provided, which offers the advantages that both the precursors used, the products obtained and the final material are not harmful to health and the environment, and its production method is simple, fast and less expensive, as well as scalable; among other advantages that will be disclosed throughout the description.

[0014] DESCRIPTION OF THE INVENTION

[0015] The invention relates to a method for manufacturing mixed oxide precursors, characterized by the addition of specific compounds that are mixed at "high shear", and subsequently heat-treated at the temperature and time required for each particular mixed oxide in question in order to transform its crystalline structure into the desired one, specific temperature and times that are established in the scientific-technical literature for each mixed oxide according to the crystalline structure that is desired to be induced by the heat treatment.

[0016] According to the invention, "high shear" is defined as mixing or grinding by means of equipment that disperses and grinds substances, at an agitation speed of at least 400 rpm.

[0017] A first aspect of the invention relates to the method of obtaining mixed oxide precursors, wherein the method comprises the steps of: a) mixing an organic acid salt of at least two metals or at least two organic acid salts of different metals, preferably where the metals are bonded to C, O and / or H; a nonpolar medium which is an oil, a surfactant, and a polar medium selected from water or a polar organic solvent; wherein the metals of the organic acid salt or salts are in stoichiometric proportion with respect to the stoichiometry of the metals in the mixed oxides to be obtained, b) mixing and grinding the mixture obtained in step (a) at high shear at at least 400 rpm for at least 2 minutes, preferably for 2 to 30 minutes, more preferably for 2 to 20 minutes, and even more preferably for 4 to 12 minutes.

[0018] The main advantages of the method are that both the starting materials and the products obtained with this method are not harmful to health or the environment, and, in addition, the production method is simpler, faster, less expensive and more easily scalable than any of those known to date in the state of the art.

[0019] According to the invention, "mixed oxide" is defined as an oxide suitable for the manufacture of battery cathodes, preferably comprising:

[0020] - at least one alkali metal (monovalent) and / or at least one divalent metal

[0021] - at least one metal selected from among transition metals.

[0022] The alkali metal is preferably lithium, sodium, potassium, or combinations thereof, but not limited to these. The divalent metal is preferably magnesium, calcium, zinc, or combinations thereof, but not limited to these. The transition metal is preferably nickel, manganese, iron, cobalt, or combinations thereof, but not limited to these.

[0023] Preferably, these mixed oxides have a particle size of less than 100 pm.

[0024] Particle size refers to the average diameter of the mixed oxide particles, which, in the present invention, has been measured using scanning electron microscopy (SEM). It is defined as the average value of the longest axis of the particle for all mixed oxide particles observed in the same SEM image. Alternatively, this particle size could be measured using techniques other than SEM, such as transmission electron microscopy (TEM), X-ray diffraction (XRD), or laser diffraction granulometry, among others.

[0025] Also, preferably, these mixed oxides have a crystalline structure consisting of a layered structure, although they may have other types of crystalline structure, for example, and without limitation, spinels, divinas, tunnel-type oxides, etc.

[0026] According to the invention, a "layered structure" is defined as one formed by an alternating succession of layers (laminae) of metal oxides and layers of alkali metals, with weak atomic bonds between layers. This structure is optimal for intercalation reactions.

[0027] The crystalline structure (e.g., layered crystalline structure) that characterizes the mixed oxide particles of your invention can be determined by different characterization techniques, such as XRD or TEM.

[0028] A preferred embodiment of the invention relates to the method where the organic acid salt or salts are selected from a salt of an organic acid of 1 to 6 carbon atoms, and even more preferably are independently selected from acetate, carbonate, or citrate.

[0029] An even more preferred embodiment of the invention relates to the method where the organic acid salt or salts are acetate.

[0030] Another preferred embodiment of the invention relates to the method where the metal of the salt or organic acid salts added in step a) is an alkali metal, i.e. selected from lithium, sodium, potassium, rubidium, cesium, francium, or any combination thereof, preferably an organic salt of lithium and / or sodium, such as for example a lithium and / or sodium acetate.

[0031] The presence of sodium in the organic acid salt (e.g., sodium acetate) used in the synthesis method results in the production of a sodium mixed oxide precursor. These sodium mixed oxides are useful for manufacturing cathodes for sodium-ion batteries (though not limited to this type of battery). Furthermore, the presence of sodium in the cathodes offers the advantages of being less toxic than lithium, being abundant in nature and therefore having relatively low raw material costs, and enabling fast charging, stability at extreme temperatures, and protection against overheating or thermal runaway. However, sodium cathodes have a lower energy density than lithium cathodes, storing less energy per unit weight. They also have lower efficiency and a shorter lifespan.

[0032] A further preferred embodiment of the invention relates to the method where at least one of the metals of the salt or organic acid salts (for example, a metal acetate) added in step a) is a monovalent alkali metal and at least one other of the metals of the salt or organic acid salts is an alkaline earth metal and / or a transition metal.

[0033] In a further preferred embodiment, the salt or salts are acetate, the alkali metal is lithium and / or sodium, the alkaline earth metal is magnesium, and / or the transition metal is selected from nickel, manganese, cobalt, iron, or combinations thereof. Such organic acid salts (e.g., metal acetates) may also be of other alkali metals, alkaline earth metals, or transition metals, respectively.

[0034] Preferably, at least one sodium organic acid salt and at least one nickel, magnesium, and / or manganese organic acid salt are added. The presence of these four metals (Na, Ni, Mg, Mn) in the organic acid salt results in the formation of mixed oxide precursors of these four metals, which, together in the mixed oxides, provide the advantage of resulting in a layered structure with excellent electrochemical behavior in sodium ion charge-discharge processes.

[0035] An example of a mixed oxide obtainable from mixed oxide precursors comprising these four metals has the chemical formula NaO.66NiO.27MGOO6MNO.66O2. This specific composition is a layered sodium oxide and is considered one of the most promising materials for sodium-ion battery cathodes. Furthermore, the addition of magnesium in these quantities stabilizes the network and prevents unwanted phase transitions during charging.

[0036] Other non-limiting examples of mixed oxides synthesizable from the precursors obtained according to the method of the present invention are simple mixed oxides (e.g., L₂MnOs, with a monoclinic structure), mixed oxides with non-layered structures (e.g., Li₁₂Mn₂O₄, with a spinel-type cubic structure), or complex mixed oxides (e.g., Li₁₂Mn₀₆Ni₂O₂, Li₁₂Mn₀₆Co₀₂O₂, or Li₁₂Mn₀₂Co₀₆O₂). In summary, the metal of the organic acid salt according to the invention can be any metal, although preferably it will be an alkali and / or alkaline earth and / or transition metal, more preferably sodium; even more preferably sodium, magnesium, manganese, nickel, cobalt, and their combinations; and still more preferably, combinations of organic acid salts of the four preceding metals.Preferably, this organic acid salt is a metallic acetate, although it could also be other organic acid salts such as metallic citrates, metallic carbonates, or combinations thereof.

[0037] Acetates are solids (preferably in powder form) and their addition is controlled by weight (e.g., using a digital scale). Using acetates as reagents is very convenient because they are composed of a metal, oxygen, hydrogen, and carbon. This allows for the removal of non-metallic components from the acetate through the formation of H₂O and CO₂ at relatively low temperatures (e.g., around 120°C would be sufficient to remove the water, and around 400°C to remove the carbon) during heating. Therefore, in the heating stage for obtaining mixed oxides from precursors at elevated temperatures (e.g., from 500°C or around 900°C as non-limiting examples), the loss of the non-metallic part of the acetates will be rapid. Another advantage of using acetates is that they are not harmful to health or the environment, unlike some other precursors that are.Other additional advantages of adding acetates are that they are easily miscible and that the use of acetates results in non-harmful and easily disposed of reaction products.

[0038] In a preferred embodiment, the nonpolar medium in step a) is selected from petrolatum, coconut oil, motor oil (mineral, synthetic, or semi-synthetic), and paraffin oil; and is preferably petrolatum; although it can also be any nonpolar medium with hydrophobic properties known in the prior art. Petrolatum acts as the nonpolar organic medium and provides the hydrophobic component, with the advantage that it is non-toxic, non-irritating, and non-corrosive. Furthermore, this compound would be removed during the heating of the precursors for the subsequent combustion of the mixed oxides, yielding CO and / or CO2 as combustion products, thus eliminating this impurity from the final mixed oxide obtained.Alternatively to petroleum jelly, other organic media could also be added, such as oils like coconut oil, paraffin oils, or motor oils.

[0039] In another preferred embodiment, the surfactant in step a) is selected from oleic acid, glycerol, dodecyl sulfate, and amines; preferably oleic acid, although it can also be any organic surfactant with one hydrophilic and one hydrophobic end. Oleic acid acts as a surfactant and offers the advantages of being non-toxic, even with repeated exposure, and non-harmful to health and corrosive. Furthermore, this compound would be removed during the heating of the precursors for the subsequent combustion of the mixed oxides, yielding CO and / or CO2 as combustion products, thus eliminating this impurity from the final mixed oxide. Alternatively to oleic acid, other surfactants such as glycerol, dodecyl sulfates (such as sodium dodecyl sulfate (SDS)), amines, and, in general, any anti-corrosive organic compound could also be added.

[0040] In a further preferred embodiment, the nonpolar medium added in step a) is petrolatum and the surfactant added in step a) is oleic acid. In fact, in the present invention, it has been observed that the nonpolar medium, petrolatum, and the surfactant, oleic acid, act synergistically in step a). This synergistic effect is the formation of an emulsion, which is rapidly achieved and homogenized by high-shear milling and subsequent synthesis of the mixed oxides (by heating the precursors to obtain the mixed oxides).

[0041] This effect occurs because the metal ions (from organic acid salts such as metal acetates) are hydrophilic, and therefore dissolve in the polar medium inside micelles formed with the help of oleic acid as a surfactant due to its amphipathic nature, with its polar part oriented towards the interior of the micelle and its nonpolar part towards the exterior. The micelles will have an aqueous interior containing the metal ions, while the exterior will contain the nonpolar medium (for example, petrolatum). This allows an emulsion to form after the high-shear milling of step b), facilitating the rapid and efficient formation of mixed oxides (for example, in as little as 2 minutes), which is then heat-treated (for example, in a furnace) to obtain the desired final structure. In another preferred embodiment, the polar medium added in step a) is water.Water acts as a polar dispersion medium, and distilled water is preferred to avoid the addition of other metal ions that would act as impurities in the final powder. The advantage of using water as a dispersion medium is its strong hydrophilic nature, its abundance and low cost, and its non-toxicity. Other alternative polar dispersion media could be polar organic solvents such as methanol, ethanol, etc.

[0042] In step a), all the compounds mentioned above are mixed in stoichiometric proportions, which are defined as the quantitative relationships between reactants so that the chemical reaction of interest occurs, preferably in the exact amounts of each reactant, thus ensuring that, after obtaining the products, no reactants are left over.

[0043] Preferably, these stoichiometric proportions of the method of the invention refer to the fact that the initially added quantity of each of the metals (metals that have been introduced in step a) by means of their corresponding organic acid salt), correspond to the quantities (stoichiometry) of said metals in the final mixed oxide to be obtained with the precursor, since after the subsequent necessary heating stage of the precursors for obtaining the mixed oxide all the organic part of the material is burned and / or degraded.

[0044] Specifically, these stoichiometric proportions are in accordance with the following reaction stoichiometry:

[0045] (Start, precursors of departure)

[0046] CxHy(A,B)Oz+H2O+C¡HjOk+CnH2n + 2 — >

[0047] (Intermediate, after the high shear mixing process)

[0048] — >CxHyOz + AaBbOc+H2O+C¡HjOk +CnH2n+2 — >

[0049] (Final, after heat treatment in the oven)

[0050] ^•A a BbOc+H2O(v)'|'+H2(g)'|'+COx(g)'|'

[0051] Where:

[0052] A = alkali and / or alkaline earth metal

[0053] B = metal or transition metals, v = vapor, g = gas. In step b), high-shear grinding is carried out for at least 2 minutes, although at least 4 minutes is also considered, preferably between 2 and 30 minutes, more preferably between 2 and 20 minutes, and even more preferably between 4 and 12 minutes. High shear promotes the rapid, homogeneous, and uniform formation of micelles, resulting in the formation of the desired emulsion. In fact, with just at least 2 minutes of high-shear grinding in step b), with the consequent savings in time and energy, the method obtains mixed oxides suitable for cathode manufacturing.

[0054] This grinding can be carried out with any equipment capable of applying high shear, that is, dispersing and grinding substances, for example, by using blades that rotate at a high speed, i.e., a stirring or grinding speed of at least 400 rpm, preferably between 500 rpm and 20,000 rpm, more preferably between 1,000 rpm and 17,500 rpm, even more preferably between 7,000 rpm and 15,000 rpm, and still more preferably between 7,400 rpm and 15,000 rpm. The equipment will preferably be an industrial high-shear mixer or blender.

[0055] Conversely, the use of equipment with a lower shear rate, for example, a ball mill, not only fails to provide such high shear, without the corresponding advantages mentioned above, but also, as the inventors themselves have verified, requires about 90-120 minutes for grinding, which is much slower and causes excessive heating of the emulsion that can lead to its deterioration.

[0056] In fact, the use of high shear in the grinding stage b) (compared to using other mixing and grinding methods with medium or low shear below 400 rpm), for the same volume of mixture and final quantity of mixed oxides obtained, results in: a decrease in mixing time (approximately 20 times less), energy consumption (approximately 40 times less), and the cost of the necessary equipment (approximately 500 times less compared to a planetary ball mill). Indeed, the use of high shear allows for energy savings, not only due to the shorter mixing time, but also because of the reduced power required to operate the high-shear mixer compared to other techniques. Furthermore, the use of high shear allows for greater control over the emulsion's evolution, facilitating the optimization of the synthesis method.Reducing processing time does not compromise process efficiency, as the amount of unreacted precursors observed in the final product is comparable to that obtained with other conventional mixed oxide synthesis methods.

[0057] Using shear speeds greater than 500 rpm, especially in the specific range of 7,000–15,000 rpm, offers the advantage of reducing mixing time while ensuring the homogeneity and uniformity of the resulting emulsion, minimizing the possibility of overheating that could lead to its deterioration. Furthermore, it results in energy savings.

[0058] In a preferred embodiment, step b) of mixing and grinding is carried out at room temperature (between 17-27 °C) and atmospheric pressure (approx. 1 atm), thus avoiding the use of additional equipment with the consequent savings in time and costs.

[0059] Preferably, the mixture resulting from stage b) of mixing and grinding is poured into a container for subsequent heat treatment or heating in stage c). This container may be any container of any shape and material, provided that the container does not melt during the heating stage, i.e., a container that does not melt at a temperature below 1200 °C. Preferably, these containers are made of refractory ceramic material or alumina and may be of any shape.

[0060] A second aspect of the invention is a method for obtaining a mixed oxide comprising lithium characterized in that it comprises the steps (a) and (b) described above, and additionally the following step: c) heating the mixture obtained in step (b) to a temperature of between 500-900 °C for a time of between 3 and 30 h.

[0061] Other non-limiting examples of synthesizable mixed oxides according to the invention are simple mixed oxides (e.g., L^MnOs, with a monoclinic structure), mixed oxides with non-layered structures (e.g., L¡Mn2O4, with a spinel-type cubic structure), or complex mixed oxides (e.g., Li1.2Mno.6Nio.2O2, Li1.2Mn0.6Co0.2O2 or L¡ 1 2M no.2Coo.6O2).

[0062] A third aspect is a method for obtaining a mixed oxide comprising sodium characterized in that it comprises the steps (a) and (b) described above, and additionally the following step: c) heating the mixture obtained in step (b) to a temperature between 700-1200 °C for a time between 6 and 30 h.

[0063] An example of a mixed oxide comprising four metals has the chemical formula NaO.66NiO.27MGO.06MNO.66O2. This specific composition is a sodium oxide lamellar and is considered one of the most promising materials for sodium-ion battery cathodes. Furthermore, the addition of magnesium in these quantities stabilizes the grid and prevents unwanted phase transitions during charging.

[0064] In any stage c) of the present invention, the powder resulting from milling, the mixed oxide precursor, is treated at a higher temperature to obtain the desired crystalline structure for the mixed oxides (for example, a layered crystalline structure), thus obtaining the product. Both the temperature and heating time are established in the scientific and technical literature for the correct formation of the desired crystalline structure in the mixed oxide through this heating stage. These temperatures and heating times will also be determined according to the particle size of the mixed oxide to be obtained after heating in stage c). By way of non-limiting example, this heating could be, for example, at 900 °C for 10 hours.

[0065] Overall, the mixing method that yields the mixed oxide precursor emulsion, which, when heat-treated, results in the final products suitable for cathode manufacturing (comprising steps a) is rapid (as little as 2 minutes), which is faster than other conventional processes for obtaining mixed oxide precursors, such as sol-gel routes, which take approximately 12 hours. All of this is achieved without affecting the efficiency of mixed oxide manufacturing (the final product), which is comparable to that of other conventional techniques.

[0066] Another advantage is that the mixing stage does not require pressure or temperature (the latter being optional), which simplifies the method and reduces the number of variables to control. Furthermore, the method is straightforward and does not require expensive infrastructure or equipment (for example, a high-shear mixer; a mixer is inexpensive), unlike other prior art processes that use elements such as autoclaves, rotary evaporators, ultrasonic probes, etc. This simplicity and lower cost of the manufacturing method according to the invention allows for easy and inexpensive scaling up, requiring only resizing the high-shear mixer and the vessels used. Conversely, scaling up is not straightforward for other prior art methods due to their greater complexity and cost, which is highly relevant given the high demand for this type of mixed oxide suitable for cathode manufacturing.

[0067] In another preferred embodiment, prior to heating step c) and after pouring step b) of the mixture, an additional preheating step c1) is carried out at a temperature between 100 °C and 120 °C for a period of between 30 minutes and 2 hours, preferably at 120 °C for 1 hour. This preheating step allows the removal of water before the heat treatment step d), which is carried out at a higher temperature. This prevents the presence of water during the main heating step d), which, in principle, allows for greater control of the synthesis reaction of the mixed oxides suitable for manufacturing cathodes of the invention during step d).

[0068] In another preferred embodiment, prior to heating step c) but after step b) or step c1), additional preheating c2) is performed at a temperature between 350 and 450 °C for a period of between 30 minutes and 5 hours, preferably at 400 °C for 1 hour. This heating allows for the removal of organic compounds through combustion, thus eliminating the organic medium (e.g., petrolatum) and the surfactant (e.g., oleic acid) present, which decompose into CO and CO2. In other words, this preheating step allows for the removal of these organic compounds before the heat treatment step d), which is carried out at a higher temperature.This prevents the presence of these organic compounds during the main heating stage d), which in principle allows for greater control of the synthesis reaction of the mixed oxides suitable for the manufacture of cathodes of the invention during stage d).

[0069] A further preferred embodiment comprises combining the three warm-ups: namely, specifically a first warm-up d) at 100-120 °C for 30-120 minutes; a second warm-up c2) at 350-450 °C for 30-300 minutes; and a third and final warm-up c).

[0070] An even more preferred embodiment comprises performing a single heating to the temperature required for step c), omitting steps c1 and c2, with the consequent saving of energy and time.

[0071] Another preferred embodiment comprises performing the heating of step c) in a furnace, and after heating, allowing the resulting mixed oxide to cool to room temperature inside the furnace with the furnace turned off. The advantage of this, in contrast to removing the sample from the furnace and placing it directly in a room-temperature environment, is that it avoids thermal shock that can cause deterioration of the container and loss of the contained material, as well as stabilizing the crystalline structure of interest.

[0072] Another aspect of the invention relates to the battery cathode comprising the mixed oxides obtained according to the method of the invention. Of particular interest are the cathodes comprising sodium oxides, and even more particularly those comprising NaO.66NiO.27MGO O6MNO.66O2, as these are among the most promising cathode materials for sodium-ion batteries.

[0073] Throughout the description and claims, the word "comprises" and its variations are not intended to exclude other technical features, additives, components, or steps. For those skilled in the art, other objects, advantages, and features of the invention will become apparent partly from the description and partly from the practice of the invention. The following examples and figures are provided for illustrative purposes and are not intended to limit the scope of the present invention.

[0074] BRIEF DESCRIPTION OF THE FIGURES

[0075] Figure 1.- Powder X-ray spectrometer obtained for mixed oxide particles of composition NaO.66NiO.27MGOO6MNO.66O2 and with a layered crystalline structure, synthesized according to Example 1 of the invention, the synthesis of which initially comprises mixing different metal acetates (of Ni, Mg, Mn, and Na) with oleic acid, petrolatum, and water, and stirring the mixture at 15,000 rpm for 4 minutes. Figure 2.- SEM image obtained at 10,000x magnification for the mixed oxide particles of composition NaO.66NiO.27MGOO6MNO.66O2 and with a layered crystalline structure according to Example 1 of the invention.

[0076] Figure 3.- a) High-angle brightfield mode image and EDX composition maps for the mixed oxide particles of composition Nao.66Nio.27Mgo.06Mno.66O2 and of layered crystalline structure according to example 1 of the invention, obtained by scanning transmission electron microscopy; b) Integrated EDX spectrum of the area marked with a square in a).

[0077] Figure 4.- Powder X-ray spectrometer obtained for mixed oxide particles of composition Nao.66Nio.27Mgoo6Mno.66O2 and of layered crystalline structure, synthesized according to example 1 of the invention, beating the mixture of initial compounds at different times and speeds, specifically for 4, 8 or 12 minutes, at (a) 7,400 rpm, (b) 8,350 rpm, (c) 11,000 rpm, (d) 12,700 rpm and (e) 15,000 rpm.

[0078] Figure 5.- Electrochemical characterization of cathodes produced from mixed oxide particles of composition NaO.66NiO.27MGOO6MNO.66O2 and of layered crystalline structure, synthesized according to example 1 of the invention at 15,000 rpm for 4 minutes (sample “High Shear”), compared with an initial mixture of the compounds of the oxide synthesis method made in a ball mill at 300 rpm for 90 minutes (sample “Grinding”), (a) Galvanostatic curves, (b) discharge capacity retention curves at 0.2C and 0.5C, (c) discharge capacity retention curves in the first 50 cycles, (d) cyclic voltammetry curves, (e) open-circuit electrochemical impedance spectroscopy curves, and (f) electrochemical impedance spectroscopy curves after 100 cycles.

[0079] Figure 6.- Powder X-ray spectrometer obtained for mixed oxide particles according to example 2 of the invention, of composition (a) L^MnOs, (b) LiM^C , (c) Li,2Mno,eN¡o,2O2, (d) Li,2Mno,eCoo,2O2 and (o) Li,2Mno,2Coo,eO2.

[0080] Figure 7.- Powder X-ray spectrometer obtained for mixed oxide particles according to Example 3 of the invention, wherein the nonpolar medium (sample 1 “Motor oil” in Figure 7a), the surfactant (sample 2 “0.1 M SDS” in Figure 7b), or both, nonpolar medium and surfactant (sample 3 “Coco-glycerol” in Figure 7c), are replaced by compounds other than those used in Example 1. EXAMPLES

[0081] Example 1

[0082] The invention will now be illustrated by an example of the synthesis of a mixed oxide precursor and subsequent synthesis of a mixed oxide from said precursor obtained by the inventors, which demonstrates the effectiveness of the method of manufacturing mixed oxides suitable for cathodes of the invention.

[0083] First, stoichiometric amounts of four different metal acetates (Ni, Mg, Mn, and Na) were mixed with oleic acid, petroleum jelly, and distilled water, as shown in the following table:

[0084] The mixture was beaten at different times and revolutions per minute (RPM) using a hand mixer (Taurus BAPI 750 INOX model, 750 W), which simulates an industrial high-shear mixer. A total of 15 different mixtures (samples) were prepared using different RPMs and mixing times. Specifically, for five different RPMs (7,400, 8,350, 11,000, 12,700, or 15,000 RPM), samples were prepared at three different times (4, 8, or 12 minutes), resulting in a total of 15 samples.

[0085] As an example, the synthesis process for mixed oxides is summarized below for the sample beaten for 4 minutes at 15,000 rpm, bearing in mind that the process is identical for the other 14 samples. After beating the mixture for 4 minutes at 15,000 rpm (or the corresponding time and speed for the other samples), the mixed oxide precursor was obtained. The resulting emulsion (the mixed oxide precursor product) was poured into an alumina crucible, which was heated in an air atmosphere to 120 °C at a rate of 2 °C / min, where it was held for 1 hour to remove any remaining water. Subsequently, it was heated at the same rate to 400 °C, where it was held at a constant temperature for 1 hour to remove the carbon compounds typical of the combustion processes of petrolatum and oleic acid, which decompose into CO and CO2.

[0086] Finally, the mixed oxide precursor powder obtained in the previous step was heated to 900 °C for 10 hours to achieve the desired layered structure and then cooled to room temperature inside the oven. X-ray diffraction results for the sample mixed at 15,000 rpm for 4 minutes (see Figure 1), as well as scanning electron microscopy results for the same sample (see Figure 2) with its corresponding chemical composition spectrum measured by energy-dispersive X-ray spectroscopy (EDX) (see Figure 3), confirmed the success of the proposed synthesis method. The synthesized particles reached an average size of 1.6 ± 0.5 pm, with a truncated pyramid morphology with a hexagonal base. These particles exhibited well-defined facets and steps on their sides, indicative of their layered structure.

[0087] Particle size is defined as the mean value of the long axis for all mixed oxide particles observed in various SEM images in this case, on the same scale, measuring a minimum of 180 particles.

[0088] The Bruker “D8 ADVANCE A25” diffractometer was used for X-ray diffraction. The particles exhibited a truncated pyramid morphology with a hexagonal base, well-defined facets, and steps on the sides, space group P63 / mmc (194), indicative of their layered structure.

[0089] Figure 4 shows the X-ray diffraction results for these 15 different samples, as a function of the mixing speed and mixing time used during their synthesis. It was found that the same desired final product, NaO.66Nio.27MgoO6Mno.66O2, was obtained for all samples, although in some cases small amounts of other secondary oxides were present. This demonstrates the effectiveness of this procedure in obtaining the desired mixed oxide (in this case, NaO.66Nio.27MgoO6Mno.66O2).

[0090] Finally, cathodes made of the NaO.66Nio.27Mgo.06Mno.66O2 oxide synthesized in this Example 1 from the sample mixed at 15,000 rpm for 4 minutes (category named “high shear”) were electrochemically characterized and compared with a cathode made of the same composition and using the same synthesis procedure, with the difference that the compounds for the synthesis of the NaO.66Nio.27Mgo.06Mno.66O2 oxide were mixed in a ball mill at 300 rpm for 90 minutes, thus being at low shear (sample named “Grinding”). The low-shear “Grinding” sample is a comparative example and is not part of the invention. This electrochemical characterization is shown in Figure 5.

[0091] Figure 5a shows the galvanostatic charge / discharge cycling curves for both samples “High shear” and “Grinding”, in sodium cells.

[0092] Figure 5b shows the retention of load / unload capacity versus the number of load and unload cycles, for both samples “High Shear” and “Grinding”, obtained at 0.2C and 0.5C.

[0093] Figure 5c shows the capacity retention at different current intensities of the “Grinding” and “High Shear” samples in the first 50 charge and discharge cycles.

[0094] Figure 5d shows the cyclic voltammetry curves in the first cycle of the “Grinding” and “High Shear” samples, in sodium cells at 0.1 mV / s.

[0095] Figure 5e shows the electrochemical impedance spectroscopy (EIS) curves of the “Grinding” and “High shear” samples, under open circuit.

[0096] Figure 5f shows the electrochemical impedance spectroscopy curves of the “Grinding” and “High Shear” samples after 100 cycles.

[0097] Electrochemical characterization corroborated the electrochemical efficiency of the cathodes manufactured by this method, which, when compared with the values ​​obtained in the scientific and technical literature, offer the expected performance for these materials.

[0098] Example 2

[0099] The previous synthesis conditions of example 1 (with mixing at 15,000 rpm for 4 minutes) were used for the synthesis of transition metal oxide precursors with lithium, such as a simple oxide (Li2MnOs), which subsequently by heating the obtained precursor powder to a temperature of 800 °C for 12 hours yielded the simple mixed oxide; synthesis of a precursor of an oxide with a non-simple layered structure with a spinel-type cubic structure (LiM^C ), which by heating the obtained precursor powder to 600 °C for 10 hours in air achieves the desired structure in the mixed oxide, and it was allowed to cool to room temperature inside the oven; or more complex lithium oxide precursors (Lii,2Mno,6Ni0,202, Lii,2Mno,6Co0,202 or Lii,2Mno,2Co0,602) which, by heating the precursor powder obtained at a temperature of 800 °C for 20 hours, yields the indicated mixed oxides.

[0100] Another difference between the synthesis of these oxides and the NaO.66NiO.27MGO.06MNO.66O2 oxide from Example 1 is their different composition and stoichiometry. Therefore, to synthesize each of these five oxides, metal acetates of different metals, oleic acid as a surfactant, petrolatum as a nonpolar medium, and distilled water as a polar medium were initially mixed. Thus, the composition and stoichiometry of the initial reagent mixture for each of the five oxides, from which each mixed oxide precursor is prepared and subsequently, by the indicated heating, the mixed oxide, is shown below:

[0101] LhMnOs:

[0102] L¡Mn2O4:

[0103] Li,2Mno,eN¡o,202:

[0104] The resulting powder X-ray diffraction spectra of these 5 oxides are shown respectively in Figure 6 (a, b, c, d, e), demonstrating that their synthesis has been equally satisfactory.

[0105] Example 3

[0106] The objective of this example 3 is to prove that other nonpolar media other than petroleum jelly (such as motor oil or coconut oil), as well as other surfactant compounds other than oleic acid (such as glycerol or sodium dodecyl sulfate (SDS)), are satisfactory for the synthesis of mixed oxides according to the method of the invention.

[0107] For this purpose, in this example 3, the previous synthesis conditions of example 1 were used, with mixing at 15,000 rpm for 4 minutes, keeping distilled water as the polar medium, preparing 3 different samples with the following differences:

[0108] Sample 1 of Example 3: Replace the nonpolar medium (petroleum jelly) with motor oil, keeping oleic acid as the surfactant. This sample is called “Motor Oil” in Figure 7a.

[0109] Sample 2 of Example 3: Replace the surfactant (oleic acid) with sodium dodecyl sulfate (SDS), keeping the petrolatum oil as the nonpolar medium. This sample is called “0.1M SDS” in Figure 7b.

[0110] Sample 3 of Example 3: Substitute both the nonpolar medium (coconut oil for petroleum jelly) and the surfactant (glycerol for oleic acid). This sample is called “Coco-glycerol” in Figure 7c. The quantities of polar medium, nonpolar medium, and surfactant are the same in mL as in Example 1 (although the compound acting as the nonpolar medium and / or the surfactant changes in the samples of Example 3). The resulting X-ray diffraction spectra of powder from these 3 oxides are shown respectively in Figure 7a (sample 1), Figure 7b (sample 2), Figure 7c (sample 3), demonstrating that the synthesis of the mixed oxide precursor and subsequently the Nao.66Nio.27Mgoo6Mno.66O2 mixed oxide by heating the mixed oxide precursor powder obtained in the previous step to 900 °C for 10 hours has been equally satisfactory with different nonpolar media and / or different surfactants.

Claims

CLAIMS 1. A method for obtaining mixed oxide precursors comprising the following steps: a) mixing an organic acid salt of at least two metals or at least two organic acid salts of different metals; a nonpolar medium being an oil, a surfactant, and a polar medium selected from water or a polar organic solvent; wherein the metals of the organic acid salt or salts are in stoichiometric proportion with respect to the stoichiometry of the metals in the mixed oxides to be obtained, b) mixing and grinding the mixture obtained in step (a) at high shear at at least 400 rpm for at least 2 minutes, preferably for 2 to 30 minutes, more preferably for 2 to 20 minutes, and even more preferably for 4 to 12 minutes.

2. Method according to claim 1, wherein the salt or salts are independently selected from acetate, carbonate, or citrate.

3. Method according to claim 1 or 2, wherein the salt or salts are acetate.

4. Method according to any of claims 1 to 3, wherein the metal of the salt or salts is an alkali metal, preferably lithium and / or sodium.

5. Method according to any of claims 1 to 4, wherein at least one of the metals in the salt or salts is an alkali metal; and at least one other metal in the salt or salts is an alkaline earth metal and / or a transition metal.

6. Method according to claim 5, wherein the salt or salts are acetate, wherein the alkali metal is L and / or Na, and wherein the alkaline earth metal is Mg and / or the transition metal is selected from Mn, Ni, Co, Fe and any combinations thereof.

7. Method according to any of claims 1 to 6, wherein the nonpolar medium of step a) is selected from petroleum jelly, coconut oil, motor oil, and paraffin oil, preferably petroleum jelly.

8. Method according to any of claims 1 to 7, wherein the surfactant of the Step a) is selected from oleic acid, glycerol, dodecyl sulfate, and amines, preferably oleic acid.

9. Method according to any of claims 1 to 8, wherein the polar medium of step a) is water.

10. Method according to any of claims 1 to 9, wherein step b) is performed between 500-20,000 rpm, preferably between 7,000-15,000 rpm, and more preferably between 7,400 and 15,000 rpm.

11. Method according to any of claims 1 to 10, wherein step b) is performed at ambient temperature and atmospheric pressure.

12. Method for obtaining a mixed oxide comprising lithium characterized in that it comprises the steps (a) and (b) described in any of claims 1 to 11 and additionally the following step: c) heating the mixture obtained in step (b) to a temperature of between 500-900 °C for a time of between 3 and 30 h.

13. Method for obtaining a mixed oxide comprising sodium characterized in that it comprises the steps (a) and (b) described in any of claims 1 to 11 and additionally the following step: c) heating the mixture obtained in step (b) to a temperature of between 700-1200 °C for a time of between 6 and 30 h.

14. Method according to any of claims 12 or 13, wherein prior to step c) and subsequent to step b), a pre-heating and additional heating c1) is carried out at a temperature between 100 °C and 120 °C for a time between 30 minutes and 2 hours, preferably at 120 °C for 1 h.

15. Method according to any of claims 12 to 14, wherein prior to step c) and subsequent to step b) or step c1), additional heating c2) is carried out at a temperature between 350 °C and 450 °C for a time between 30 minutes and 5 hours, preferably at 400 °C for 1 h.

16. Method according to any of claims 12 to 15, wherein step c) is This is done in a furnace, and after heating the resulting mixed oxide is allowed to cool to room temperature inside the furnace with the furnace turned off.

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