Manganese spinels co-doped with iron and phosphorus for photo or magnetic field-assisted li-ion cells and their preparation method

Abstract

The invention relates to the field of technologies for storing electrical energy. In particular, photo- or magnetic field-assisted lithium ion cells, and more specifically, multifunctional materials that are useful as active components in the preparation of cathodes for said cells. Even more specifically, the invention relates to manganese spinels co-doped with iron and phosphorus, comprised in the formula LiMxPyFezMn1.5-wO4 (0.5≥ x ≥0), (0.1 ≥ y ≥0.03), (0.5≥ z ≥0.1), (0.5≥ w ≥0), where M is chosen from the elements manganese, nickel, cobalt and vanadium; a production method, cathodes for lithium ion cells prepared with said spinels and photo- or magnetic field-assisted Li-ion cells assembled with said cathodes. In the range of concentrations selected for carrying out the co-doping, new electrical, magnetic and optical functionalities are produced in said spinels, thereby inducing an improved electrochemical response under the effect of light or a magnetic field.

Description

[0001] Manganese spinels co-doped with iron and phosphorus for photo- or magneto-assisted Li-ion cells and their preparation method.

[0002] DESCRIPTION

[0003] The present invention relates to the field of technologies for storing electrical energy. In particular, it relates to photo- or magneto-assisted lithium-ion cells, and more specifically, to multifunctional materials useful as active components in the preparation of cathodes for such cells. Even more specifically, the present invention relates to manganese spinels co-doped with iron and phosphorus, comprised in the formula LiMxP yFezMni.5-wO4 (0.5> x >0), (0.1 > y >0.03), (0.5> z >0.1), (0.5> w >0), where M is chosen from the elements manganese, nickel, cobalt and vanadium; method of obtaining, cathodes for lithium ion cells prepared with said spinels and photo or magneto assisted Li ion cells assembled with said cathodes. In the concentration range selected to carry out the codoping, new electrical, magnetic and optical functionalities emanate in said spinels, thereby inducing an improved electrochemical response under the effect of light or magnetic field.

[0004] The next generation of rechargeable Li-ion batteries (LiBs) will need to deliver higher energy and power densities for critical applications such as electromobility. This means Li-ion cells (LiCel) must deliver higher capacity, with high charge / discharge rates at a stable, high operating voltage (greater than 4 V) without overheating, degradation, or other issues.

[0005] Currently, some research groups have proposed overcoming these problems through a new approach to LiCel technology. This involves harnessing the effect that a magnetic field and light have on conductive processes inside the electrodes and at the interfaces between them. Obviously, the functionalities of the electrode's active material, particularly the cathode, are key to achieving the necessary leap forward in these emerging technologies.

[0006] Two functionalities of the cathode active materials in LiCel that could have a strong impact on the future of electrical energy storage devices such as LIBs are the response to a magnetic field and the absorption / conversion of light energy, as reported in Scientific Reports, 2017, 7, 10534-10542 and in Journal of the Electrochemical Society, 1990, 137, 1796-1803.

[0007] In this scenario, two patents stand out. In US patent 10,910,679 B2, from the University of Chicago, in the name of authors Christopher S. Johnson and Anna Lee, a LiCel is proposed with a cathode whose active material is LiMnO, which is charged at high charge / discharge rates (2C-10C) by illuminating it with sunlight. These authors observe that, without illuminating the cathode, only 42% of the expected capacity is obtained (~65 mAh g -1) at a working voltage of 4.07 V, which corresponds to literature reports; while under white light, this value rises to 84% of the expected capacity. These authors propose a wide range of active materials that could function in this way, but none of them match the one proposed in the present invention.

[0008] On the other hand, patent WO2020 / 144142 A1 , from University College London (UCL), in the name of authors Heenan, Thomas; Shearing, Paul; Brett, Daniel and Tan, Chun, reports an example of a commercial LiCel, type Swagelok 51 , whose cathode contains L¡Mn2O4 as active material, which is subjected to the action of a static and rotating magnetic field. These inventors demonstrate that with a rotating magnetic field, the capacity of the LiCel is increased by 5% compared to the experiment carried out with a non-rotating permanent magnet.

[0009] In both cases the results are discrete because the active cathode material used is L¡Mn2O4 or a derivative thereof. It is known that these materials have a discrete optical and magnetic behavior, reason why the effect of a magnetic field or the light of the visible spectrum on the improvement of its electrochemical response, in particular the increase in capacity at high charge / discharge rates, according to this new technology, could be greater than that observed in the state of the art if these two functionalities (optical and magnetic) were developed in the active material of the cathode. To respond to this problem, the present invention proposes the codoping of L¡Mn2O4 with iron and phosphorus in a critical concentration range comprised in L¡MnxPyFezMn2O4 (0.5> x >0), (0.1 > y >0.03), (0.5> z >0.1 ), (0.5> w >0), where M is selected from the elements manganese, nickel, cobalt and vanadium.When the term “critical concentration range” is used in the present invention, it is to refer to the iron / phosphorus and manganese / dopant molar ratios necessary to develop surprising electrical, magnetic and optical functionalities in manganese spinels.

[0010] Recently, an article was published, Ind. Eng. Chem. Res. 2023, 62, 1016-1028, where the codoping of the spinel LiNio.5Mm.504 with iron and phosphorus is proposed, giving rise to the composition L¡Nio.5Mni.4667Feo.o2Po.oi3304, and its electrochemical behavior in a LiCel is evaluated. Although this work uses the same type of codoping as the present invention in terms of the nature of the codopants, that is, they use iron and phosphorus, the composition of this material is outside the range proposed in the present invention, specifically, the concentration of the dopants is well below what is proposed in the present invention. Furthermore, according to the X-ray diffraction results reported in this article, the dopants are not located in the same atomic positions as those appreciated in the present invention. Therefore, the functionalities observed in this invention are not developed.On the other hand, the method used to synthesize the L¡Nio.5Mni.4667Feo.o2Po.oi3304 material is complex in terms of the nature of the precursor, steps and equipment used; for example, the use of a hydrothermal treatment and two calcination treatments of the carbonate precursor. Additionally, the objective of the article in proposing and studying the L¡Nio.5Mni.4667Feo.o2Po.oi3304 composition was to improve the behavior of the LiNio.5Mm.5O4 cathode active material in terms of its electrochemical stability in conventional LiCel and not to develop the electrical, optical and magnetic functionalities for use in photo- or magneto-assisted LiCel.

[0011] There is no patent in the state of the art that covers the iron and phosphorus co-doping proposal of the present invention, nor the compositions of the proposed multifunctional materials.

[0012] The objective of the present invention is to teach a simple and scalable process for obtaining new multifunctional materials based on manganese spinels co-doped with iron and phosphorus, in a critical concentration range, which is not based on any prior theory. It is also an objective to provide new multifunctional materials comprised in the formula L¡MxPyFezMm.5-wO4 (0.5> x >0), (0.1 > y >0.03), (0.5> z >0.1), (0.5> w >0), where M is selected from the elements manganese, nickel, cobalt and vanadium and a use for these as cathode active materials in magnetic field assisted photo or magneto LiCel.

[0013] The novelty of this proposal lies in the composition of the multifunctional materials it comprises and the method for obtaining them. The essence of the present invention lies in the critical concentration range selected to perform the codoping and in the solid-state precursor synthesized to achieve this.

[0014] In one of its variants this method can be used to obtain manganese spinels co-doped with iron and phosphorus, comprised in the formula LiMxPyFezMnl ,5-wO4 (0.5> x >0), (0.1 > y >0.03), (0.5> z >0.1 ), (0.5> w >0), where M is chosen from among the elements manganese, nickel, cobalt and vanadium, but not limited to.

[0015] In one of its variants, the Solid State Precursor is thermally decomposed at 300-350 degrees Celsius, homogenized in a ball mill for 15-20 min and subsequently subjected to a second heat treatment in an open chamber furnace, with air flow of 9 ml / min, at a temperature of 350-450 degrees Celsius, preferably 400-450 degrees Celsius, for a time of 0.5-2 hours, preferably 1-1.5 hours, and subsequently the material obtained is spontaneously cooled to room temperature. In another of its variants, the Solid State Precursor is thermally decomposed at 500-550 degrees Celsius, homogenized in a ball mill for 15-20 min and subsequently subjected to a second heat treatment at a temperature of 800-900 degrees Celsius, preferably 850-900 degrees Celsius, for a time of 17-20 hours, preferably 17-18 hours, under an air flow of 9 ml / min and subsequently the product obtained is slowly cooled to room temperature, between 0.5 and 1 degrees Celsius / min, preferably 0.5-0.7 degrees Celsius / min.

[0016] The method allows precise control of the critical concentration range in which the codoping with iron and phosphorus takes place, necessary to obtain a capacity value under the action of a static magnetic field of 86% with respect to the theoretical value expected for manganese spinel and a capacity gain of 25% with respect to the value measured without the assistance of the static magnetic field. This fact, which does not respond to any previous theory, works in this way due to the atomic position occupied by the dopants in the crystalline structure of the manganese spinels L¡MxPyFezMm.5-wO4, where M is selected from the elements manganese, nickel, cobalt and vanadium, for the concentration range proposed in this invention (0.5> x >0), (0.1 > y >0.03), (0.5> z >0.1), (0.5> w >0), which leads to the formation of Fe-Fe clusters induced by P (see Figure 3) within the structure of the material.The inventors have found scientific evidence that these clusters are responsible for the surprising electrical (see Figure 4 and example 4), optical (see Figures 5 and 6 and example 5), magnetic (see Figure 7 and example 6) and electrochemical response observed in these materials under the influence of a static magnetic field (see Figures 8, 9 and 10, as well as example 7).

[0017] Two variants of the preparation method of the new multifunctional materials of the present invention are shown in Figures 1 and 2. To carry it out, the first step consists of obtaining a citrate-type Solid State Precursor that contains the mayohtahos metal ions (lithium, nickel, manganese, cobalt and vanadium) and the dopants (iron and phosphorus).

[0018] In one of its variants, the citrate type Solid State Precursor is synthesized by hot mixing at 70-90 degrees Celsius, preferably 85-90 degrees Celsius and under magnetic or mechanical stirring of 260-285 RPM, preferably 275-280 RPM, an aqueous solution of citric acid with the sources of the metal ions for which a citric acid / total metal ions molar ratio of 2: 1, preferably 1.5: 1, is established.

[0019] Citric acid, CeHsO?, is a water-soluble polyprotic acid containing three carboxylic groups (COOH) and a tertiary alcohol, enabling it to simultaneously form chelates with a wide variety of metals. This depends on the stoichiometric molar ratios of citric acid to total metals and the pH at which it is formed.

[0020] The above mixture is then heated to a temperature between 70 and 85 degrees Celsius, preferably 80 and 85 degrees Celsius, for 1 to 1.5 hours, preferably 0.5 to 1 hour. This step produces a homogeneous gel, which is necessary for phosphorus doping.

[0021] Subsequently, the source of the phosphorus dopant (85% aq. H3PO4) is added to the gel obtained from the previous step, considering the critical concentration range, established with respect to the major elements (lithium, nickel, cobalt, vanadium and manganese) and the iron dopant.

[0022] The above mixture is then neutralized by pre-cooling to a pH of 5-7, preferably 6-6.5, with 25% NH3 (aq) to finally precipitate by evaporation to obtain the citrate-type solid-state precursor. In the pH range where the precursor is neutralized in the aqueous state, the tri-ionized citrate [CeHsO?] 3' is not the only species present, but bi-ionized citrate [CeHeO?] is also produced. 2- in a ratio of ~5:1. The decrease in the total negative charge of citrate is what allows the entry of dihydrogen phosphate ions H2PO 4 probably coordinated to manganese (III). The versatility of the precursor lies precisely in the fact that varying the pH and the [Ni / Mn]T / [Cit]T / [PO4] ratio 3 ] the charge of the formed complex and therefore the amount of coordination centers can be controlled to ensure the concentration of dopants such as the H2PO ion 4 ' in the range of concentrations required.

[0023] In another of its variants, before neutralizing, hydrogen peroxide (H2O2) is added at 30%, to subsequently add the source of the phosphorus dopant (H3PO4 at 85%) and evaporate until the citrate type Solid State Precursor is precipitated.

[0024] Once the citrate-type solid-state precursor containing the mayohtahos metal ions and the dopants in the critical concentration range proposed in this invention has been obtained, it is thermally decomposed in two steps. In one of its variants, the precursor is thermally decomposed at 300-350 degrees Celsius, homogenized in a ball mill and subsequently calcined in an open chamber oven under an air flow of 9 ml / min, at a temperature around 350-450 degrees Celsius, preferably 400-450 degrees Celsius, for a time of 0.5-2 hours, preferably 1-1.5 hours and the obtained material is spontaneously cooled to room temperature.In another of its variants, the Precursor is thermally decomposed at 500-550 degrees Celsius, homogenized in a ball mill and subsequently treated at a temperature of around 800-900 degrees Celsius, preferably 850-900 degrees Celsius, for a time of 17-20 hours, preferably 17-18 hours, under air flow of 9 ml / min and the material obtained is slowly cooled to room temperature between 0.5 and 1 degrees Celsius / min, preferably 0.5-0.7 degrees Celsius / min.

[0025] During the development of the invention, an experimental design was used that also included the production and study of manganese spinels whose composition is not included in this invention, to use them as a reference in evaluating the advantages of the compositions contemplated in this invention. The elemental and phase composition of the materials was determined by atomic absorption and X-ray diffraction, respectively, and was similar to what was expected. The structural, electrical, magnetic, optical properties and the electrochemical behavior of the materials under the influence of a static magnetic field were evaluated (see Figures 3-10 and Examples 4-7). The response of the multifunctional materials included in this invention was surprising with respect to the undoped material and to the doped materials whose iron / phosphorus and manganese / dopant element molar ratios were not within the compositional range defined in this invention.Furthermore, the electrochemical behavior under the action of a static magnetic field was superior to that of the commercial materials also studied for comparison. These studies showed that with doping in the critical concentration range proposed in this invention, several different structural arrangements arise depending on the spinel composition (see Figure 3). Within the different compositions made, it was demonstrated that phosphorus can induce the formation of iron clusters in the manganese spinel structures. These iron clusters are responsible for providing a new double electronic excitation absorption band at 473 nm and a ferromagnetic or femmagnetic behavior in manganese spinels arising from iron-oxygen-iron, iron-oxygen-manganese and manganese-oxygen-manganese spin exchange interactions (see Figure 3).

[0026] Variants of the present invention also include cathodes made from the multifunctional materials obtained according to the method proposed in this invention and lithium ion cells assembled with these cathodes and operated under the influence of light or a static magnetic field.

[0027] In one of its variants, the cathode was prepared by mixing one of the active materials obtained according to the present invention, for example in the environment of L¡FexP compositions yMn(2-o.87x-i.45y)04 (0.5> x >0.14) (0.1 > y >0.07), with Super Black C65 carbon and polyvinyldiene fluoride in N-methylpyrrolidone in a ratio of 75:15:10% by mass with respect to the active material, under strong stirring and subsequently the homogeneous dispersion obtained was deposited on an aluminum sheet (current collector) by the Doctor Blade method. Prior to the preparation of the cathodes, the samples used as active material received a heat treatment of 600-750 degrees Celsius for 8h. This treatment was carried out to prevent surface degradation of the fine particles of the active material (nanometric < 50 nm) obtained after the decomposition of the precursor, which could mask the effect of the static magnetic field applied during the electrochemical measurements of the lithium ion cell prototypes evaluated with these materials.Using this procedure, cathode electrodes containing commercially available active materials (NMC532 and LNMO) were prepared. These materials were used as reference materials in evaluating the advantages of the compositions included in this invention.

[0028] In one of its variants, one of the materials obtained according to the present invention, for example in the environment of L¡FexP compositions yMn(2-o.87x-i.45y)04 (0.2> x >0.14) (0.1 > y >0.07) was evaluated as the cathode active material in a laboratory-scale coin cell lithium cell. Metallic lithium was used as the anode and a mixture of lithium hexafluorophosphate (LiPFe) with a concentration of 1 mol / L dissolved in ethylene carbonate and dimethyl carbonate in a mass ratio of 3:7 and vinyl carbonate at 2% by mass was used as the electrolyte. The electrolyte was supported on Celgard separator paper. Charging and discharging experiments at current rates from 2 / C to 10 C were carried out in potentiometry mode between 3 V and 4.47 V. Electrochemical tests under the influence of a static external magnetic field were performed by placing a 1.81 cm diameter, 0.5 cm high magnet with a surface magnetic field of 23 mT below the lithium cell holder (see Figure 8). The magnet was placed immediately below the surface of the holder where the electrochemical measurement is performed.The support used is the CCH-1 model from Biologic. The magnet was fixed to the surface of the support in a position where the magnetic field emanating from it passed through the surface of the button cell. The axis passing through the center of the magnet was aligned with the central axis of the receptacle where the button cell was placed for the electrochemical measurement. In this way, the presence of a stationary magnetic field was guaranteed during all electrochemical measurements. Similarly, lithium-ion cells containing cathodes made with commercially available active materials (NMC532 and LNMO) were assembled to use them as a reference in evaluating the advantages of the compositions comprised in this invention.The most notable feature to note when comparing cell behavior with and without a static magnetic field observed in these experiments is the improved capacity of approximately 15 mAh / g achieved by imposing such a magnetic field, representing a capacity gain of 25%. This capacity value is 86% of the theoretical value expected for manganese spinel operating at a voltage of 4.2 V. Furthermore, the capacity gain almost doubles the values ​​obtained with similar generic materials commercially available for lithium batteries under the same experimental conditions.

[0029] The present invention will be illustrated in detail through the following figures and embodiments.

[0030] Figure 1 shows the execution of the preparation method of doped manganese spinels, with the variant established in this invention to obtain multifunctional materials whose composition is specifically comprised of LiNio.5-y / 2PyFexMni.5-xy / 204 (0.1> x > 0.06) (0.05 > y > 0.03). The first step is to obtain a solid-state citrate-type precursor containing the majority metal ions and the dopants. The precursor is synthesized by mixing an aqueous solution of citric acid with the sources of the metal ions while hot and under magnetic or mechanical stirring. After a time under stirring and heating, a gel is formed to which the source of the phosphorus dopant is added, considering the established concentration range with respect to the majority elements and the iron dopant. Subsequently, the gel is cooled and neutralized before precipitating the solid-state citrate-type precursor by evaporation.Once the precursor is obtained, it is thermally decomposed, homogenized in a ball mill, calcined under air flow and slowly cooled.

[0031] Figure 2 shows the execution of the preparation method of doped manganese spinels, with the established vahant to obtain multifunctional materials whose composition is included in L¡FexP yMn(2-o.87x-i.45y)04 (0.5> x >0.14) (0.1 > y >0.07). The first step of the method is similar to that of Figure 1 , except that 30% hydrogen peroxide (H2O2) is added after the incorporation of the salts containing the metals and the phosphoric acid, and before raising the pH to a value between 6 and 6.5. Once the citrate-type Solid State Precursor is obtained, containing the majority metal ions and the dopants in the selected concentration range, it is thermally decomposed, homogenized in a ball mill, calcined in an open chamber furnace with air flow, and spontaneously cooled.

[0032] Figure 3 shows the refined Rietveld structural models of the samples prepared according to the present invention. In (a) a doped spinel, the composition of which does not match the concentration range proposed in this invention, specifically the composition LiP yMn2O4 (0.1 > and >0.04) and in (b) a doped spinel, whose composition is included in this interval, specifically LiFe x P yMn(2-o.87x- i.45y)O4 (0.2> x >0.1 ) (0.1 > y >0.07). The coordinations and atomic positions of each ionic species present in each spinel are shown on the right side of Figures 3(a) and 3(b). Rietveld structural refinement indicates that in all materials the phosphorus (P) atoms occupy a tetrahedral position 48f, with the coordinate (1 / 8, 1 / 8, 0.338) for sample (a) and (1 / 8, 1 / 8, 0.3661 ) for sample (b). In sample (b) iron (III) (Fe) occupies only the 16d position. On the left side of Figure 3(c) it is highlighted how the strength of the phosphorus-oxygen-iron bonds (between double and triple bonds) favors the approximation of iron (III) ions to form the iron clusters described in the present invention. On the right side, the double electronic excitation suffered by the iron (III) ions coupled electronically and magnetically to form two e- / h+ pairs by the action of photons of wavelength 473 nm is exemplified.

[0033] Figure 4 shows the electrical behavior between 265 K and 300 K of four spinels prepared according to the present invention, for compositions comprised in L¡FexPyMn(2-0.87x-1.45y)04 (0.5> x >0) (0.1 > y >0.07), specifically a spinel doped only with phosphorus (x=0) and three spinels doped with iron and phosphorus where x=0.14, 0.25 and 0.5. In the example shown in section a), the variation in conductivity (n) with the inverse of the temperature is shown for the sample with x=0 (black line), x=0.14 (red line), x=0.25 (green line) and x=0.5 (blue line). In the example shown in section b), the variation in the concentration of charge carriers (n e ) as iron concentration increases.

[0034] Figure 5 shows the deconvoluted absorption spectra of the spinels prepared according to the present invention. In (a) a doped spinel, whose composition does not match the concentration range proposed in this invention, specifically LiP y Mn2-i.4yO4 (0.1 > y >0.04) and in (b), a doped spinel, whose composition is included in this interval, specifically L¡Fe x PyMn(2-o.87x- i.45y)O4 (0.2> x >0.1 ) (0.1 > y >0.07). The various electronic transitions are indicated by symbols. The electronic transitions in the region between 200 and 300 nm correspond to transitions between the O(2p) band and the d orbital band of manganese (Mn). The Mn transitions 4+ ( 4 A2- 4 Ti) at 336 nm and Mn 4+ ( 4 A2- 4 Ti) at 405 nm, occur between the t2g and e states g of the Mn 4+ . The Mn transitions 3+ ( 5 AND- 5 T2) at 513 nm and Mn 3+ (5 AND- 3 Ti) at 613 nm occur between t2g and e orbitals g of the Mn 3+ and by charge relocation in the t2g orbital (3t2g 1 and g 1 - (t2g 2 t2g 1 )and g 1 ) of Mn 3+ , respectively. The new transition emanating from doping, corresponding to a double electronic excitation (2 6 A1 (S)- 2 4 T1 (G)), which is observed as an absorption band at 473 nm.

[0035] Figure 6 shows the changes that occur in the width of the forbidden bands O(2p)-t2g and t2g-e g of the manganese spinels doped with iron and phosphorus in the range of compositions included in this invention as the iron content varies.

[0036] Figure 7 shows the magnetic behavior of manganese spinels prepared according to the present invention. In (a) the magnetization behavior during cooling with field (FC) and without field (ZFC) is shown for the compositions L¡FexPyMn(2-0.87x-1.45y)04 (0.5> x >0) (0.1 > y >0.07) and in (b) the variation of the effective magnetic moment (meff) with the iron (Fe) composition.

[0037] Figure 8 shows a drawing of the electrochemical measurement system under the influence of a magnetic field. The coin cell (1 ) is shown, placed in a Biologic brand CCH-1 support (2) and the 23 mT magnet (3). The magnet was fixed immediately below the surface of the support where the electrochemical measurement is performed. The support used is the Biologic brand CCH-1 model. The magnet was attached to the surface of the support in a position where the magnetic field emanating from it passes through the surface of the lithium cell (1 ). The axis passing through the center of the magnet was made to coincide with the central axis of the CCH-1 support where the lithium cell is seated for the electrochemical measurement. In this way, the presence of a static magnetic field was guaranteed during all electrochemical measurements.

[0038] Figure 9 shows the 50th charge / discharge cycle of a lithium cell in high power (2C) regime, recorded under the influence of a static external magnetic field of 23 mT (red) and without a magnetic field (black). This lithium cell was assembled according to example 7 of the present invention, with a cathode prepared in the manner shown in example 3 of this invention with an active material whose composition is comprised in L¡FexPyMn(2-0.87x-1.45y)04 (0.2> x >0.14) (0.1 > y >0.07).

[0039] Figure 10 shows the operation of different lithium-ion cells, operating at different current rates (C / 2-10C), under the influence of a static magnetic field of 23 mT and without this. In (a) the behavior of the lithium cell assembled according to example 7 and a cathode prepared according to example 3 of the present invention is shown, whose active material has a composition comprised in L¡FexPyMri(2-o.87x-i.45y)04 (0.2> x >0.14) (0.1 > y >0.07). In (b) and (c) the lithium-ion cells assembled according to example 7 of this invention, with cathodes prepared according to example 3 of the present invention, whose active material is commercial NMC532 (LiNio.5Mno.3Coo.2O2) and commercial LNMO (LiNio.5Mm.5O4), respectively.

[0040] Example No. 1

[0041] To a volume of 60 liters of distilled water is added 3.17 kg of citric acid (CeHsO?) and maintained for 5 minutes under continuous magnetic or mechanical stirring of 280 RPM and heating at 85 degrees Celsius. To the previous solution is added 0.223 kg of lithium carbonate (Li2CO3), 0.244 kg of nickel hydroxide (Ni(OH)2), 0.929 kg of manganese carbonate (MnCOs) and 1 liter of an aqueous solution of iron (III) nitrate nonahydrate (Fe(NO3)3.9H2O) of concentration 0.5 mol / l maintaining continuous magnetic or mechanical stirring of 280 RPM and heating at 85 degrees Celsius for 1 hour. Subsequently, maintaining magnetic or mechanical stirring at 280 RPM, the gel formed in the previous step is allowed to cool to room temperature and 0.150 liters of phosphoric acid (H3PO4) at 85% are added.Magnetic or mechanical stirring is maintained at 280 RPM for an additional 5 minutes before neutralizing the gel to a pH of 6 by slowly adding 3 liters of a 25% ammonia (NH3) solution. The gel is then evaporated at 85 degrees Celsius under continuous magnetic or mechanical stirring at 280 RPM. In the second stage of the synthesis, the precursor is thermally decomposed at 500 degrees Celsius, homogenized in a ball mill for 15 minutes, and subsequently calcined to a temperature of 850 degrees Celsius at a heating rate of 10 degrees Celsius / min and under an air flow of 9 ml / min for 17 hours. The resulting material is then slowly cooled at 0.6 degrees Celsius / min to room temperature.

[0042] Example No. 2

[0043] To a volume of 30 liters of distilled water is added 3.23 kg of citric acid (CeHsO?) and maintained for 5 minutes under continuous magnetic or mechanical stirring of 280 RPM and heating of 85 degrees Celsius. To the previous solution is added 1.74 liters of an aqueous solution of iron (III) nitrate nonahydrate (Fe (NOs) 3 * 9H 2 O) of concentration 0.5 mol / l, maintaining continuous magnetic or mechanical stirring of 280 RPM and heating at 85 degrees Celsius for 10 minutes, after which 0.210 kg of lithium carbonate (Li 2 CO 3) and 1.203 kg of manganese carbonate (MnCO s) are added, maintaining magnetic or mechanical stirring of 280 RPM and heating of 85 degrees Celsius for 20 more minutes. Subsequently, it is allowed to cool to room temperature and 2 liters of 30% hydrogen peroxide (H2O2) are added under continuous magnetic or mechanical stirring.Magnetic or mechanical stirring is maintained at 280 RPM for 5 more minutes before neutralizing the gel to a pH value of 5.5 by slowly adding a 25% ammonia (NH3) solution. In the second stage of the synthesis, the precursor is thermally decomposed at 300 degrees Celsius, homogenized in a ball mill for 20 minutes and subsequently calcined in an open chamber furnace, up to a temperature of 430 degrees Celsius at a heating rate of 10 degrees Celsius / min and this temperature is maintained for 1 hour. Subsequently, the obtained material is spontaneously cooled to room temperature.

[0044] Example No. 3

[0045] One of the active materials obtained according to the present invention, for example one comprised in the composition L¡FexP yMn(2-0.87x-1.45y)04 (0.2> x >0.14) (0.1 > y >0.07) was subjected to a heat treatment of 500-750 degrees Celsius for 8 hours prior to the preparation of cathodes for lithium ion cells. To prepare the cathodes with the composition material L¡FexP yMn(2-o.87x-i.45y)04 (0.2> x >0.14) (0.1 > y >0.07) and the commercial active materials NMC532 and LNMO the following steps were followed: in a container the active material, polyvinyldiene fluoride and Super Black C65 carbon are mixed in a ratio of 75:15:10% by mass, respectively. The polyvinyldiene fluoride is added from a solution of the same in N-methylpyrrolidone whose composition can range between 5 and 10%. The mixture is placed in a “Thinky are-250 mixer” mixing equipment and under intense stirring for 30 seconds at 500 RPM and then for 5 minutes at 1500 RPM. Subsequently, the dispersion is deposited on an aluminum sheet using the Doctor Blade method, ensuring that the layer thickness is between 20-25 microns. The electrode deposited on the aluminum collector is dried at 50 degrees Celsius for 3-5 hours and once dry it is cut into 11 mm diameter discs.Before assembling the lithium-ion cells, the electrodes cut into discs are kept for 12 hours under heating at 90 degrees Celsius and vacuum.

[0046] Example No. 4

[0047] Measurement of the electrical properties of four spinels prepared according to the present invention, for compositions comprised in L¡FexP yMn(2-o.87x-i.45y)04 (0.5> x >0) (0.1> y >0.07), specifically a spinel doped only with phosphorus (x=0) and three spinels doped with iron and phosphorus, where x=0.14, 0.25 and 0.5, was carried out on an electrical measurements probe in the temperature range of 265K to 300K by the Hall and Van Der Paw effect techniques. All experiments were carried out with a temperature control that guarantees ± 0.001 K, with a Lakeshore 336 and electrical measurements were recorded with a Keithley 2636B system. Pure samples were pressed at 7MPa using polyvinyl acid as a binder and formed as discs with a diameter of 0.9 cm and a thickness of 0.4 mm. The discs were sintered at 500 °C for 4 hours. The four Pt electrical contacts were then placed on the surface of the disc-shaped samples, bonded with silver paint, and once dry, measurements were started. The results of this study are shown in Figure 4.The example shown in section a) shows the variation in conductivity (o) with the inverse of temperature for the spinel doped only with phosphorus x=0 (black line) and for the three spinels codoped with iron and phosphorus, x=0.14 (red line), x=0.25 (green line) and x=0.5 (blue line). The example shown in section b) shows the variation in the concentration of charge carriers (n. e) as the iron concentration increases. The authors of this invention found a surprising increase (of one order of magnitude) in the electronic conductivity of manganese spinels whose compositions are within the proposed range (x=0.14-0.5) with respect to spinel whose composition is outside this range (x=0). This behavior is beneficial when using the materials proposed in this invention in lithium cells since it would reduce ohmic potential losses and heat generation in cells operating at high charge / discharge rates, which is a current requirement for this technology. As can be seen in Figure 4b, the increase in electronic conductivity is due to an increase of between 1 and 2 orders of magnitude in the electron concentration (n e ) in these materials. This remarkable increase is associated with a higher number of electrons provided by iron (III) (d 5) when it replaces manganese (III) (d 4 ) in these spinels. Another reason underlying this behavior is a decrease in the width of the forbidden band (band transition: O(2 P )-t2g, see example 5, figure 6), due to the unique phosphorus-iron interaction observed in the spinels whose compositions are in the critical range proposed in this invention for doping, which contributes to a greater presence of Ü2 electrons P for driving. Example No. 5

[0048] The measurement of the optical properties of two spinels obtained according to the present invention, one of them whose composition is included in the concentration range proposed to carry out the codoping in this invention L¡Fe x PyMn(2-o.87x- i.45y)O4 (0.5> x >0.14) (0.1 > y >0.07) and another outside this interval LiP yMn2-i.42yO4 (0.1 > and >0.04), is performed by UV-Vis on a PerkinElmer spectrometer in the reflectance mode between 200 and 1200 nm. The absorption coefficient is calculated following the KubelKa-Munk equation, while the Tauc plot method is used to determine the gap energies (AE). The results of this study are shown in Figure 5. Overall, the spectrum of the LiP sample y Mn2-i.42yO4 (0.1 > y >0.04) is characterized by overlapping electronic transitions arising from oxygen ions (O 2- ) to manganese (III) and (IV) ions, as well as electronic transitions between the d orbitals of the metal ions. It is important to note that this material has acceptable optical absorption in most of the visible region, with a peak within the 300-700 nm and 700-1200 nm regions. The first region is particularly characterized by transitions that mainly involve O(2 P )-Mn 3+ , O(2 P)-Mn 4+ as well as Mn 3+ (dd) and Mn 4+ (dd). While the region between 700-1200 nm is influenced by electronic transitions between non-degenerate orbitals, for example, due to the Jahn-Teller distortion affecting Mn(III) in an octahedral environment, according to J. Opt. Soc. Am. B, 1999, 16, 475-483.

[0049] In the work published in Nature Communications, 2019, 10, 4946-4953, it was shown that it is possible to considerably improve the charge and discharge rate of LiMn2O4, as well as its capacity in a lithium battery, by using an external light source. This occurs because some of its electronic transitions involve the formation of the polaron (Mn 3+ )* represented by equation 1:

[0050] Mn 3+ + hv = (Mn 3+ )*= Mn 4+ + e- Equation 1

[0051] As can be seen in Figure 5, the light-induced polaron formation increases by substituting Mn(III) for Fe(III) in the spinel L¡FexP y Mn(2-0.87x-1.45y)04 (0.5> x >0.14) (0.1 > y >0.07). This is evidenced by the appearance of a new band around 473 nm that is not observed in the LiP sample. y Mn2-i.42yO4 (0.1 > y >0.04). This band only appears when a magnetic spin coupling occurs between Fe(III) ions (ferromagnetic interaction) through a spin exchange interaction, according to Physical Review B, 1998, 57, 2203-2216. Since each absorbed photon with a wavelength of 473 nm is responsible for the excitation of two electrons from the t2g band to the e band g, it can be considered that doping manganese spinels according to the present invention makes it possible to increase the generation of electron-hole pairs in this type of materials. This could have a significant impact on the commercial use of the materials proposed in this invention in electrochemical devices such as those described in US patent 10,910,679 B2. Additionally, Figure 6 shows the changes that occur in the width of the O(2p)-t2g and t2g-e bands. g of the spinels doped with iron and phosphorus in the range of compositions included in this invention. As can be seen in this Figure, the optical gap (O(2 P )-t2g ) decreases between 2.2 and 2.0 eV with increasing iron content, while the band width (t2g- e g ) increases between 1.3 eV and 1.6 eV.

[0052] Example No. 6

[0053] Measurement of the magnetic properties of manganese spinels with compositions ranging from L¡Fe x PyMn(2-o.87x-i.45y)04 (0.5> x >0) (0.1> y >0.07), specifically a phosphorus-only doped spinel (x=0) and three iron-phosphorus codoped spinels where x=0.14, 0.25 and 0.5, was performed on the Quantum Design MPMS3 apparatus. Magnetization curves during field (FC) and field-free (ZFC) cooling are recorded by first cooling the samples from 300 K to 2 K under zero magnetic field and then measuring the magnetic moment as the temperature was increased from 2 K to 300 K under a direct current (DC) using a scan rate of 10 K min -1. The experimental susceptibility values ​​( / ) are corrected for the diamagnetic contribution by using Pascal's constant. The results of this study are shown in Figure 7. (a) The magnetization behavior during field (FC) and field-free (ZFC) cooling is shown, and (b) the variation of the effective magnetic moment (meff) with increasing iron content. This Figure shows an example of another functionality (ferromagnetism / ferhmagnetism) emanating from manganese spinels, from room temperature to low temperatures, after codoping with iron and phosphorus in the critical concentration range proposed in this invention.As can be seen in this Figure, the behavior of spinel doped only with phosphorus (x=0) is not surprising, but is similar to L¡Mn2O4, that is, it exhibits paramagnetic behavior from room temperature to around 47 K, where paramagnetic / antiferromagnetic transitions occur. For spinels whose compositions are within L¡FexP. yMn(2-o.87x-i.45y)04 (0.5> x >0.1 ) (0.1 > y >0.07), specifically for (x=0.14-0.5), surprisingly the presence of a ferromagnetic interaction is observed in the variation of the susceptibility vs temperature due to the oxygen-iron-oxygen (O-Fe-O) exchange interactions. This is evidenced by the higher values ​​of susceptibility and magnetic moment at different temperatures of these codoped spinels compared to the spinel doped only with phosphorus (x=0). Since no impurity of another magnetic phase, such as iron and manganese oxide (MnFe2O4) or magnetite (Fe3Ü4), was detected by the X-ray diffraction technique, experimental evidence suggests that the magnetic response of manganese spinels co-doped with iron and phosphorus, in the concentration range proposed in this invention, is an intrinsic property of these new multifunctional materials.The ferromagnetic interaction between iron atoms observed through these magnetic and UV-Visible measurements (reflected in Example 5) is the basis of the net ferromagnetic / ferrimagnetic behavior observed in the manganese spinels object of this invention. These interactions have been observed only in these manganese spinels codoped with iron and phosphorus. The inventors have obtained scientific evidence that the separate doping of manganese spinels with iron or phosphorus does not modify the magnetic behavior of these materials.

[0054] Example No. 7

[0055] The cathodes prepared according to Example 3 of this invention were inserted into a laboratory-scale coin-type lithium cell, together with a metallic lithium anode and an electrolyte composed of a mixture of lithium hexafluorophosphate with a concentration of 1 mol / L and vinyl carbonate (2% by weight) in ethylene carbonate and dimethyl carbonate (mass ratio 3:7). 140 pl of the electrolyte were deposited on the porous Celgard paper that serves as a separator between the cathode electrode and the metallic lithium. Charge and discharge experiments at current rates of 2 / C up to 10 C were performed in potentiometric mode between 3 V and 4.47 V. Electrochemical tests under the influence of a static external magnetic field were performed by placing a 1.81 cm diameter and 0.5 cm high magnet with a magnetic field on its surface of 23 mT below the lithium cell support (see Figure 8).The magnet was placed immediately below the surface of the support where the electrochemical measurement is performed. The support used is the CCH-1 model from Biologic. The magnet was fixed to the surface of the support in a position in which the magnetic field emanating from it passes through the surface of the button cell. The axis passing through the center of the magnet was made to coincide with the central axis of the receptacle where the button cell is seated for the electrochemical measurement. In this way, the presence of a stationary magnetic field was guaranteed during all electrochemical measurements. The notable improvements that can be obtained by providing a 23 mT magnetic stimulus to a lithium cell assembled with an iron- and phosphorus-doped manganese spinel, in the concentration range proposed in this invention, specifically for the compositions comprised in L¡FexP. yMn(2-o.87x-i.45y)04 (0.2> x >0.1 ) (0.1 > y >0.07), can be verified in Figures 9 and 10. In Figure 9, the most notable feature to take into account when comparing the behavior of the lithium cell with and without a static magnetic field is the improved capacity of approximately 15 mAh / g achieved by imposing the magnetic field, which represents a capacity gain of 25%. This capacity value under the action of a static magnetic field is 86% of the theoretical value expected for manganese spinel operating at a voltage of 4.2 V. On the other hand, the capacity gain doubles the values ​​obtained with similar generic materials commercially available for lithium batteries under the same experimental conditions, as can be verified in Figure 10.For lithium ion cells assembled with commercial materials such as NMC532 and LNMO, it was found that the capacity increases were very small or none when cycling the lithium ion cells, in high power regime under the influence of a static external magnetic field of 23 mT, according to the present invention. For example, for NMC532 (see Fig. 10(b)) the capacity improvement at 558 mA / g is only 6 mAh / g, which is less than half of the capacity gain observed in the codoped spinels according to the present invention at a current of half the value (296 mA / g) (see Fig. 10(a)). On the other hand, for the lithium cell assembled with the commercial LNMO material (see Fig. 10(c)), the capacity gain of the material is only 3.5 mA / g at 2C (296 mA / g) under a static magnetic field of 23 mT, that is, between three and four times lower than that observed for one of the compositions included in the range proposed in this invention L¡FexP. yMn(2-0.87x-i.45y)04 (0.2> x >0.14) (0.1 > y >0.07) at the same cycling current value. An additional difference, observed in this Figure, is in the behavior of the lithium ion cells under a static magnetic field of 23 mT, assembled with the commercial LNMO material and with one of the compositions within the range proposed in this invention, LiFe x P y Mn(2- o.87x-i .45y)04 (0.2> x >0.14) (0.1 > y >0.07), resides in the way the magnetic field causes enhancements for different cycling rates. While in general for the material proposed in the present invention the capacity gain increases as the current rate increases; for the commercial LNMO material the highest capacity gains are observed at low current rates.

Claims

Manganese spinels co-doped with iron and phosphorus for photo- or magneto-assisted Li-ion cells and their preparation method. CLAIMS 1. Multifunctional materials based on manganese spinels co-doped with iron and phosphorus, comprised in the formula L¡MxPyFezMm.5-wO4 (0.5> x >0), (0.1 > y >0.03), (0.5> z >0.1), (0.5> w >0) where M is selected from the elements manganese, nickel, cobalt and vanadium.

2. Multifunctional materials based on manganese spinels co-doped with iron and phosphorus according to claim 1, characterized in that the two doping elements are in a molar concentration ratio between them and with respect to manganese of: Fe / P=2, P / Mn=0.04-0.06; Fe / Mn=0.08-0.

35.

3. Multifunctional materials based on manganese spinels co-doped with iron and phosphorus according to claim 1, characterized in that the iron is located in 16d octahedral sites of the spinel's crystalline structure.

4. Multifunctional materials based on manganese spinels co-doped with iron and phosphorus according to claim 1, characterized in that the phosphorus is located in tetrahedral sites 48f of the spinel's crystalline structure.

5. Multifunctional materials based on manganese spinels co-doped with iron and phosphorus according to claim 1, characterized by the existence of iron clusters in the crystalline structure of the spinel.

6. Multifunctional materials based on manganese spinels co-doped with iron and phosphorus according to claim 1, characterized by an electronic conductivity of 10' 5 -10' 6 S / cm.

7. Multifunctional materials based on manganese spinels co-doped with iron and phosphorus according to claim 1, characterized by a double electronic excitation absorption band at 473 nm.

8. Multifunctional materials based on manganese spinels co-doped with iron and phosphorus according to claim 1, characterized by femmagnetic / ferromagnetic behavior from room temperature to low temperatures.

9. Method for preparing multifunctional materials based on manganese spinels codoped with iron and phosphorus, comprised in the formula L¡MxPyFezMm.5-wO4 (0.5> x >0), (0.1 > y >0.03), (0.5> z >0.1 ), (0.5> w >0), where M It is selected from the elements manganese, nickel, cobalt and vanadium, characterized in that it comprises: 1) synthesis, 2) thermal decomposition, 3) grinding, 4) calcination and 5) cooling of a citrate type Solid State Precursor containing the major elements and the dopants, for which the following are preferably used as raw material: Li2CO3 (as a lithium source), Ni(OH)2 (as a nickel source), MnCOs (as a manganese source), Fe(NOs)3*9H2O (as an iron source) and H3PO4 (as a phosphorus source), following the following steps: a) Prepare an aqueous solution of citric acid and maintain under magnetic or mechanical stirring and heating for 5-15 min. b) Add the salts containing the major metal ions and the iron dopant to the solution formed in step a) maintaining magnetic or mechanical stirring and heating for 0.5-1.5 hours. c) Add the phosphorus source to the mixture described in step b) maintaining magnetic or mechanical stirring and heating for 5-15 min.d) Neutralize the mixture described in step c) with a 25% ammonia solution while maintaining magnetic or mechanical stirring. e) Evaporate the gel formed in step d) while maintaining magnetic or mechanical stirring to obtain the citrate-type solid-state precursor. f) Decompose, grind, and calcine the precursor obtained in step e). g) Cool the product obtained in step f) to obtain the multifunctional materials based on manganese spinels co-doped with iron and phosphorus.

10. Preparation method described in claim 9, characterized in that the concentration of the citric acid solution mentioned in step a) is 0.27-0.3 mol / l.

11. Preparation method described in claim 9, characterized in that the magnetic or mechanical stirring mentioned in steps a) to e) is 280 RPM.

12. Preparation method described in claim 9, characterized in that the heating mentioned in steps a) to e) is carried out at a temperature value between 80-85 degrees Celsius.

13. Preparation method described in claim 9, characterized in that the most optimal time interval mentioned in steps a) and c) is 10-15 minutes.

14. Preparation method described in claim 9, characterized in that the most optimal time interval mentioned in step b) is 1-1.5 hours.

15. Preparation method described in claim 9, characterized in that the neutralization mentioned in step d) is carried out at a pH of 5-6.

5.

16. Preparation method described in claim 9, characterized in that before adjusting the pH, 2-4 ml of hydrogen peroxide (H2O2) is optionally added.

17. Preparation method described in claim 9, characterized in that the decomposition step of the precursor mentioned in step f) is carried out at a temperature in the range of 300 to 500 degrees Celsius and for a time of 1 to 2 hours.

18. Preparation method described in claim 9, characterized in that the grinding step mentioned in step f) is carried out in a ball mill for 15-20 minutes.

19. Preparation method described in claim 9, characterized in that the calcination step mentioned in step f) is carried out at a temperature in the range of 400 to 900 degrees Celsius, for a time of 1 to 20 hours with air flow of 9-12 ml / minute.

20. Preparation method described in claim 9, characterized in that the calcination product is cooled to room temperature at a rate of 0.5-0.7 degrees Celsius / minute.

21. Cathodes for photo- or magneto-assisted lithium ion cells characterized in that the electrochemically active material is the multifunctional material according to claims 1-8.

22. Lithium ion cell with response induced by the application of a magnetic field, characterized in that it comprises the cathode (1) according to claim 21 and a 23 mT magnet (3).

23. Lithium ion cell with response induced by the application of a magnetic field, according to claim 22, characterized in that the magnet (3) can be static or rotating.

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