Method for preparing micrometric lithium iron phosphate

Abstract

The invention primarily relates to a method for preparing lithium iron phosphate (LiFePO4) particles having a micrometric morphology from a source of iron cations and phosphate anions, the method comprising preparing primary iron phosphate (FePO4.xH2O) particles, followed by obtaining secondary LiFePO4 particles through subsequent lithiation and calcination of the primary particles. The invention also relates to the use of lithium iron phosphate (LiFePO4) particles having a micrometric morphology as obtained by means of the aforementioned method as a cathode material, and to the cathode material. The invention is defined in the claims.

Description

[0001] PROCESS FOR PREPARING MICROMETRIC LITHIUM IRON PHOSPHATE

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to the field of electrochemistry; it relates more particularly to the production of a so-called "advanced" cathode material, incorporating lithium ferric phosphate LiFePO4 (LFP) prepared using different grades of phosphoric acid as raw material, i.e. a phosphoric acid comprising various duly selected metallic and / or metalloid microelements. The invention further provides a method of producing LFP adjusted according to each additive.

[0004] CONTEXT OF THE INVENTION

[0005] Due to the sharp decline in fossil fuel reserves and the increasing energy demand of modern civilization, several international organizations and institutes have taken a keen interest in the rapid development of several technologies such as lithium-ion batteries.

[0006] Lithium-ion batteries are the most advanced electrochemical energy storage and conversion system and are used in hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and stationary energy storage for solar and wind power generation and smart grids.

[0007] Several materials such as lithium nickel cobalt aluminum oxides (NCA), lithium nickel manganese cobalt oxides (NMC), lithium transition materials (LMO), and manganese-based spinel compounds have emerged; after lithium cobalt oxide LiCoO2 was commercialized by Sony in the early 1990s [1],

[0008] LiFePO4 material was first reported in 1997 as a cathode material for lithium-ion batteries by Goodenough and colleagues. Commercialized materials include the current generation of lithium-ion batteries using the LiCoO2 cathode material, which cannot meet the cost, environmental, and safety requirements of high-power applications.

[0009] Olivine-structured phosphate materials LiFePO4 are commercialized as cathode materials in secondary lithium-ion batteries. Due to their low cost, high thermal and chemical stability, cycling stability and high theoretical capacity of 170 mAhg-1, this material is very interesting for application in electric vehicles. However, like any material, LFP suffers from several drawbacks. First of all, an energy density in practice (and in theory) lower than that of LiCoO2, for commercial materials we obtain 165 mAh.g-1 (for a theoretical capacity of 170 mAh / g) but associated with a lower operating voltage. Secondly, the low electronic conductivity of the material severely limits the charge / discharge regimes (limited to C / 50) without specific treatment.

[0010] Several research studies have opted for various solutions to improve certain properties of LFPs, such as coating the surface particles, reducing the particle size and doping the LFP material with cations and anions. Coating the surface of LiFePO4 particles with various conductive substances is a method that not only protects the surface but also improves the electronic conduction properties while maintaining ionic conductivity. This makes it possible to achieve operating regimes of several C in commercial versions; and to improve cyclability.

[0011] Several techniques are used to manufacture carbon-coated LiFePO4, such as gel-coating and a carbo-thermal technique. These techniques optimize the amount of carbon in the structure of the active material. The coating of the LFP particles is done either in-situ (during material preparation) or mixed with the binder, etc.

[0012] Particle size has a significant effect on the properties of the cathode material, as the nanoparticle-based material improves electrochemical performance by reducing ionic and electronic diffusion distances.

[0013] To combine the effect of carbon coating and particle size reduction, several researches have focused on using porous carbon as a template to form nanoscale LiFePO4 / C with excellent electrochemical performance.

[0014] Patent EP 2270903Al[2] describes the hydrothermal production of LFP active material using Li, Fe salt and phosphoric acid as raw materials. The possibility of controlling the average size of primary particles equal to or greater than 30 nm and equal to or less than 100 nm is described in this invention. Based on this invention, controlling the amount of Li and Fe elements added to the P element has made it possible to reduce and control the size of crystalline particles of LiFePO4.

[0015] Patent EP1553647A1 [3] discloses a method for producing the cathode material LiFePO4 by solid-state route for a secondary battery, using metallic iron, phosphoric acid and lithium hydroxide as precursors. The manufacture of LiFePO4 was carried out by a first calcination from room temperature to 300-450°C, followed by a second calcination from room temperature to the calcination completion temperature. A second synthesis step was carried out by adding a carbon source followed by a calcination step.

[0016] Heteroelement doping (substitution) is also considered as a possible approach to improve intrinsic conductivity, but unlike the mentioned methods, it suffers from a decrease in breakdown density. Doping with cations and anions is commonly used for LiFePO4 modification without reducing absorption density. This method is considered as one of the effective approaches to improve the high-rate performance of LiFePO4 material. Doping of the Li site is important to improve the electrochemical properties of LiFePO4. It has been found that LiFePO4 has a one-dimensional diffusion pathway of lithium ions, which could be closed by the Li site doped with high-valent transition metal ions, resulting in low electrochemical efficiency.

[0017] Doping elements such as F and S in carbon films improves the electrochemical performance of composites. This is due to the behavior of heteroatoms which can not only act as electron donors to provide charge carriers but also create crystal defects, which facilitates the transport of Li+ in the carbon film. Doping with anions can directly affect the intrinsic electrical properties [4], Different anions such as sulfur, nitrogen, chlorine, and fluorine are known to be practically important doping anions.

[0018] The stabilization of the crystal structure of the LiFePO4 cathode material and the improvement of the transport of electrons and Li+ ions are achieved by doping the Fe site of the LiFel- xMxP04 cathode material (M=Ni, Co, Ti, Al, Mg, Zn and K, etc.). In addition, supervalent cations such as Mn4+ and Pt4+ improve the electronic conductivity and the diffusion coefficient of Li+ and, consequently, the electrochemical performance of the material.

[0019] Patent No. EP2360117B1 [5] discloses a method for manufacturing LiFePO4 having an average particle diameter of 50 to 550 nm, and an average secondary particle diameter of 5 to 100 mm with a porosity of 15 to 40 The material developed within the scope of this invention is characterized by the following formula Lil+aFel-x Mx(PO4-b)Xb, with:

[0020] M: Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, Y

[0021] X: F, S, N

[0022] -0.5 <a<+0.5; 0<x<0.5; and 0<b<0.1 Cette invention a montré que l'amélioration de la densité énergétique des matériaux cathodiques est assurée par une conductivité électrique élevée, une structure cristalline stable et des particules de plus petite taille.

[0023] The present invention consists of a simple and efficient approach leading to the elaboration of LiFePO4 particles optimally combining dimensions of said particles and porosity. It is based on the effect of duly selected cationic and anionic additives or microelements, present in or incorporated into phosphoric acid and on their synergistic effect on the properties of the resulting LFP cathode material, such as conductivity, packing density and cycling performance. The present invention is further suitable for large-scale production of LFP.

[0024] DESCRIPTION OF THE INVENTION

[0025] The present invention relates to the large-scale production of an advanced LiFePO4 (LFP) cathode material characterized by high purity and controlled morphology by using different additives or microelements such as Na, F, S, Mg, Zn, K, Cl, Al, Ca, Co, Cr, Fe, K, Mn, Mo, Ni, Ti, V, Cd and As present in phosphoric acid or in the source of ferrous salts. In the context of the present invention, these additives (microelements) can be either of exogenous origin, i.e. added, in a predetermined amount to the phosphoric acid, during the process, or of endogenous origin, i.e. originally present depending on the origin or the quality or grade of the phosphoric acid used. By natural mineral material is meant the ores themselves or the mining waste used as a source of phosphorus during the industrial production of phosphoric acid.

[0026] The invention also aims to improve the performance of LiFePO4 at low temperature (-20°C), as well as to improve the conductivity, charge density and diffusion coefficient of lithium.

[0027] The preparation of the large-scale cathode material (4L and 50L) using the CSTR reactor was carried out by a simple and uncomplicated coprecipitation method. The synthesis process consisted of two main steps: first, the preparation of primary FePO4 particles by coprecipitation, using phosphoric acid with different additive contents (Fig. 1). The second step is the preparation of secondary LiFePO4 particles by solid reaction or spray drying (Fig. 2).

[0028] The additive-rich phosphoric acid can take advantage of the synergistic effects of cationic and anionic elements, thus inducing the improvement of the electrochemical properties of the highly nanoporous morphology with micrometer-sized particles. The present invention consists of the study of the synergistic effect of all the additives Na, F, S, Mg, Zn, K, Cl, Al, Ca, Co, Cr, Fe, K, Mn, Mo, Ni, Ti, V, Cd and As on the conductivity, sampling density, stability and cycling performance of LFPs in particular.

[0029] In addition, the effect of each additive was also evaluated, and the precipitation of each element under FePO4 production conditions was also monitored.

[0030] In this invention, a formulation of LFP production according to each additive is proposed, in order to adapt each type of phosphoric acid to LFP production.

[0031] This work highlights the importance of the synergistic effect of cations and anions and provides a new methodology for the selection of cationic and anionic additives or microelements for the development of advanced LFP cathode materials.

[0032] BRIEF DESCRIPTION OF FIGURES AND TABLES

[0033] The following detailed description, together with the accompanying figures and tables, will provide a better understanding of the above-mentioned and other objects, features and advantages of the present invention, wherein:

[0034] Figure 1. Production of lithium iron phosphate (LFP) using a CSTR reactor.

[0035] Figure 2. Rietveld refinement of the advanced cathode material LiFePO4.

[0036] Figure 3. SEM image of FePO4, xH2O as a function of synthesis time.

[0037] Figure 4. SEM images of the surface and cross-section of the advanced LiFePO4 cathode material.

[0038] Figure 5. Typical charge / discharge profiles of the advanced cathode material LiFePO4 using the spray drying approach for the lithiation step (C / 10, electrode composition (LFP / CB / PVDF: 85 / 10 / 5)-lM LiPF6, EC-DEC, mass loading: 1.50 mg / cm2).

[0039] Figure 6. Capacity retention of LiFeP04 advanced cathode using spray drying approach for lithiation step (C / 10, electrode composition (LFP / CB / PVDF: 85 / 10 / 5)-lM LiPF6 EC-DEC, electrode weight: 1.50 mg / cm2).

[0040] Table 1. Densities of developed and commercial LFP materials.

[0041] Table 2. Different additives used in the synthesis of the FePO4 precursor.

[0042] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention focuses on the large-scale production of LFP by two-step coprecipitation, by studying the effect of cationic and anionic additives such as Na, F, S, Mg, Zn, K, Cl, Al, Ca, Co, Cr, Fe, K, Mn, Mo, Ni, Ti, V, Cd, and As, on the properties of LFP and its electrochemical performance.

[0043] The invention comprises the following steps:

[0044] • Preparation of the FePO4 precursor by coprecipitation

[0045] • Insertion of additives during the formation / nucleation of secondary particles of the FePO4 precursor

[0046] • In situ coating step of FePO4-C secondary particles

[0047] • Formation of the LiFePO4 product from FePO4 and a lithium and carbon source, by carrying out a combined carbonization-lithiation step of the FePO4-C precursor

[0048] The synthesis of the advanced LFP cathode material, as schematized in Figure 1, was carried out by coprecipitation in two facile steps using a CSTR reactor with a capacity of 4 and 50 L. The first step consists of manufacturing the FePO4 precursor by coprecipitation by pumping a mixture of phosphate and iron precursors.

[0049] According to Figure 1, a carbon source such as glucose or conductive polymers were dissolved in distilled water and placed in the reactor first. This step coats the primary particles and improves the conductivity of the cathode material without increasing its production cost.

[0050] Different phosphate sources can be used such as H3PO4, NH4H2PO4, (NH4)2HPO4, or (NH4)3PO4 with a P concentration of 2M and a preparation volume of 0.5L. Different additives based on Na, F, S, Mg, Zn, K, Cl, Al, Ca, Co, Cr, Fe, K, Mn, Mo, Ni, Ti, V, Cd, and As were added at different concentrations ranging from 0.1 to 400 ppm to improve the conductivity, density, and electrochemical capacity of the advanced material at temperatures of -20°C. The additive derivatives used can be alkaline earth metal hydroxides, alkali metal hydroxides, or ammonia compounds.

[0051] An iron solution of IM concentration was prepared in IL volume from several iron derivatives such as FeSO4, FeC2O4 - 2H2O, FeCI2, Fe2(SO4)3, FeCI3 or Fe(NO3)3.

[0052] The mixture of the different solutions was kept under continuous stirring before being pumped into the reactor with a flow rate of 300 ml / h. The pH control of the reaction mixture at 2.5-3 in Examples 1, 2 and 3 was achieved by pumping an ammonia solution NH3, H2O with a concentration of 2M, or by using an organic base which serves as a coprecipitating agent for FePO4 and at the same time as a carbon source for the in situ coating of the primary particles.

[0053] The reaction was kept stirring at 1000 rpm and at a temperature of 55°C for 20 hours. During the synthesis, different samples were taken at different times to determine the chemical composition of the filtrates and to characterize the different powders obtained by XRD, SEM and BET. After 20 hours of reaction, the mixture was separated by filtration and washed for several cycles with 25 L of distilled water. The yellowish FePO4, xH2O powder obtained was dried at 80°C for 24 h, then calcined at 550°C for 10 h under an inert atmosphere.

[0054] The lithiation and carbonization process of FePO4 precursor was applied in the second step of synthesis by solid reaction or spray drying. A stoichiometric amount of FePO4 and Li2CO3 were well mixed by solid reaction using a ball mill under a stirring speed of 180 rpm for 2 hours, with the addition of glucose (15 wt%) and acetone as solvent. The resulting product was dried at 80 °C, then calcined and carbonized in an inert atmosphere at 700 °C for 10 hours.

[0055] For the spray-drying approach, a solution containing a stoichiometric amount of FePO4, LiOH, 10% citric acid, and glucose (15% by weight) was prepared and sprayed at 110 °C into fine droplets and dried instantly into solid particles. The calcination conditions were similar to those used for solid reaction lithiation.

[0056] According to Figure 2, the use of phosphoric acid with a combination of some additives such as F, S, Na, Mg, Zn and K has no effect on the purity and crystallinity of the formed LFP cathode material. This was confirmed by the phase refinement obtained by the Rietveld method, which indicates high purity and crystallinity of the material obtained in Example 6 in an orthorhombic system.

[0057] The analysis of the morphology of the FePO4 material obtained in Example 4 by SEM (Figure 3), showed that at t=0, the material is composed of several nanometric particles, and no agglomeration was detected. From 2h of synthesis, a very weak agglomeration of particles was formed. The agglomeration was remarkably detected after 5h of synthesis. However, after 20 hours, the agglomerated particles were dissociated.

[0058] The SEM images in Figure 4 of the LFP obtained in Example 5 show a porous appearance on the surface and cross-section. These results demonstrate that the pores and voids between the LFP particles provide space for the electrolyte, which has a very significant impact on the electrochemical performance of the cathode material.

[0059] Furthermore, in this invention, we have demonstrated that it is possible to obtain the agglomerated form of LFP obtained in Example 6 by using FeSO4 as the iron source, which is less expensive than Fe(NO3)3 or others.

[0060] The electrochemical performance of the LFP cathode material obtained in Examples 5 and 6 was measured in a coin-type half-cell at 25°C. The produced LFP material is characterized by a high specific discharge capacity of approximately 156 mAh / g with a flat voltage plateau at 3.4 V at a C rate of 0.1C (Figure 5), and a stable Coulomb efficiency (Figure 6).

[0061] The produced LFP material exhibits low polarization, indicating a more energy-efficient electrode. The electrochemical behavior of the material is due to its pure phase, the presence of additives (F, Na, S, Mg, Zn, and K), and the agglomerated morphology, which favors the penetration of the electrolyte into the material and ensures good lithium insertion / deinsertion during galvanostatic charge / discharge cycles.

[0062] As part of this invention, it was essential to measure the density of the different materials obtained and compare them with the commercial LFP (Table 1). The values ​​obtained indicate that the advanced LFP material produced by the method described above is characterized by a higher density (1.31 g / mL) compared to the commercial LFP (0.95 g / mL).

[0063] These results can be explained by:

[0064] • In-situ coating during the FePO4 synthesis process

[0065] • Purity of the cathode material,

[0066] • Agglomerated and porous morphology of LFP,

[0067] • Presence of additives (F, Na, S, Mg, Zn and K)

[0068] • Combination of the lithiation-carbonization process (spray drying, use of citric acid, etc.)

[0069] EXAMPLES

[0070] The examples in this section serve only to illustrate the present invention and should not be construed as limiting the scope or spirit of the invention.

[0071] Example 1 The synthesis of advanced LFP cathode material in CSTR reactor was carried out as follows: initially, a mass of 15% carbon source (glucose, carbon nanotube...etc) was dissolved in water and placed in the reactor.

[0072] A 1M molar concentration of iron precursor (FeSO4,7H2O) was dissolved in distilled water (IL). Then, 0.5 L of phosphoric acid (2M) was added to the iron solution while stirring continuously, in the presence of additives Na, S, F, Mg, Zn and K, etc. (Table 2). Then, the oxidizing agent H2O2 (0.6 equimolar) was added dropwise to the previously prepared mixture. The prepared mixture was pumped at a flow rate of 360 ml / h into the reactor under a stirring speed of 450 rpm and a temperature of 60°C for 30 minutes. The initial pH was -0.2.

[0073] Then, NH3, H2O solution (2M) was pumped into the reactor to adjust the pH of the mixture to 2.5-3. After the ammonia solution was added, the mixture turned yellow-white in color. The reaction mixture was kept stirring at 1000 rpm.

[0074] During the synthesis, it was essential to take different samples from 0.5h to 20h, to determine the chemical elements present in the solutions after filtration by ICP, and to analyze the powders obtained (FePO4, xH2O) by XRD, SEM, BET, etc.

[0075] Example 2

[0076] The two solutions of iron (FeSO4, 7H2O(1M)) and phosphoric acid (2M) were prepared separately. Then, the oxidant H2O2 (0.6 equimolar) was added dropwise to the iron solution, and the additives of Na, F, S, Mg, Zn, K, Cl, Al, Ca, Co, Cr, Fe, K, Mn, Mo, Ni, Ti, V, Cd, and As with a concentration ranging from 0.1 to 400 ppm were added to the phosphoric acid solution.

[0077] A carbon source was dissolved in distilled water and placed in the reactor. The two solutions of iron and phosphoric acid were pumped in parallel with a flow rate of 300 ml / h and 600 ml / h respectively, with continuous stirring at 450 rpm for 30 minutes at a temperature of 55 °C.

[0078] At the same time, pH control at the target value 2.5-3 of the reaction mixture was carried out by continuously pumping organic base or ammonia solution NH3, H2O (2M) under continuous stirring at 1000 rpm and a temperature of 55 °C. Throughout the reaction, from 0.5 to 20 hours, a series of samples were taken.

[0079] Example 3 A phosphoric acid solution (2M) was prepared in a volume of 0.5L, in the presence of a separate additive as shown in the table below. 1 mole of a Fe2+ solution was prepared separately in a volume of IL. Then, the agent H2O2 (0.6 equimolar) was added to the iron solution, to oxidize the Fe2+ ions to Fe3+.

[0080] The two solutions of iron and phosphoric acid were thoroughly mixed before being pumped into the reactor.

[0081] Then, a carbon source was dissolved in distilled water and placed in the reactor, before pumping the mixture of the two solutions of iron and phosphoric acid with a constant flow rate of 300 ml / h under continuous stirring of 405 rpm and a temperature of 55 °C. The pH control between 2.5 and 3 of the reaction mixture was carried out by pumping the ammonia solution NH3, H2O (2M) under continuous stirring of 1000 rpm for the entire duration of the reaction (20 hours).

[0082] The different filtrates collected during the reaction (0.5-20 hours) were analyzed by ICP, and the powders obtained were analyzed by DRX, SEM, BET...etc.

[0083] Example 4

[0084] The FePO4, xH2O product obtained in Examples 1, 2 and 3 was separated by filter press by applying several successive washes with 25 liters of distilled water for 35 minutes. The product obtained was dried in an oven at 80°C for 12 hours. To pass from the amorphous phase to the crystalline phase. The FePO4, xH2O material formed was calcined in a tubular furnace at 550°C for 10 hours under a nitrogen atmosphere.

[0085] Example 5

[0086] The one-step lithiation-carbonization process was carried out by solid reaction. For this purpose, a stoichiometric amount of FePO4 obtained in Example 4 with Li2CO3 was well mixed in the ball mill at a speed of 180 rpm for 2 hours; at the same time, glucose (15%) and acetone were added to the mixture. The resulting product was calcined and carbonized in a tube furnace under nitrogen atmosphere at 700°C for 10 hours.

[0087] Example 6 The spray drying method was used for the lithiation process of the FePO4 precursor obtained in Example 4. For this purpose, a solution containing a stoichiometric amount of FePO4-C material, LiOH, 10% citric acid, and glucose (15% by weight) was prepared at a temperature of 25°C and with continuous stirring. The prepared precursor solution was sprayed into fine droplets and then flash-dried into solid particles at 110°C for 12 hours. The resulting solid product was calcined and carbonized in a tube furnace under an inert atmosphere at a temperature of 700°C for 10 hours.

[0088] Example 7

[0089] The preparation of the electrode of the active material LiFePO4-C was carried out by mixing the material obtained in Examples 5 and 6 with carbon black and polyvinylidene fluoride (PVDF) in a weight ratio of 85:10:5.

[0090] To form the suspension electrode, the three powders were mixed with N-Methyl-2-Pyrrolidone (NMP). The resulting mixture was then deposited on aluminum as a current collector. The formed suspension was dried at 60 °C to evaporate the NMP solvent. A second drying is required at 80 °C under vacuum for 24 hours.

[0091] Before starting the electrochemical tests, the dried electrodes were cut and pressed. The button cell assembly was carried out in the glove box.

[0092] The prepared electrodes were used as cathodes, and the lithium foil served as the counter electrode and the reference electrode. A Whatman glass microfiber filter (grade GF / D, Whatman) was used as the separator, and the electrolyte used was a solution of LiPF6 1M in a mixture of ethylene carbonate and diethyl carbonate with a weight ratio of 1:1:1. The button cells were charged and discharged between 2.5 and 3.8 V at 25 °C with a rate of 0.1C relative to Li+ / Li.

[0093] INDUSTRIAL APPLICABILITY As described in the previous section, the production of an advanced LFP material with high energy density and high electrochemical performance was achieved in two easy steps.

[0094] Controlling the various stages of secondary LFP particle production, such as coating, addition of appropriate additives, allows producing a material with high conductivity, porosity and energy density and, consequently, high electrochemical performance.

[0095] Combining these parameters produces an electrode with improved performance and gives the batteries improved capacity and speed properties.

[0096] REFERENCES CITED IN THE DESCRIPTION

[0097] [1] J. Seher, M. Frôba, Shape Matters: The Effect of Particle Morphology on the Fast-Charging Performance of LiFePO4 / C Nanoparticle Composite Electrodes, ACS OMEGA. 6 (2021) 24062-24069. https: / / doi.org / 10.1021 / acsomega.lc03432.

[0098] [2] M. Nakano, M. Saitou, Method For Production of Cathode Active Material for Lithium Ion Battery, EP 2270903A1, 2011.

[0099] [3] S. Okada, J.-l. Yamaki, N. Hatta, I. Uchiyama, T. Inaba, Method for Preparing Positive Electrode Material for Secondary Cell, and Secondary Cell, EP001553647A1, 2005.

[0100] [4] M. Armanda, M.E.A. y de Dompablo, Benefits of N for O substitution in polyoxoanionic electrode materials : a first principles investigation of the electrochemical properties of Li2 FeSiO4-y Ny (y=0,0.5, 1), Materials Chemistry. 21 (2011) 10026-10034. https: / / doi.org / 10.1039 / c0jm04216a.

[0101] [5] S. Choy, Y.T. Lee, H.-K. Park, S.M. Park, J.E. Lee, Lithium Iron Phosphate Having an Olivine

[0102] Structure, and Preparation Method Thereof, EP236117B1, 2011. https: / / doi.Org / 10.1016 / J.MATLET.2005.12.083.

[0103] ABREGE

[0104] The invention relates to the production of a so-called "advanced" cathode material, incorporating lithium ferric phosphate LiFePO4 (LFP) of micrometric morphology, prepared using different grades of phosphoric acid as raw material comprising various metallic and / or metalloid microelements, respectively cationic and / or anionic, selected from Na, S, F, Mg, Zn, and K, Cl, Al, Ca, Co, Cr, Fe, K, Mn, Mo, Ni, Ti, V, Cd and As in particular. These microelements are either derived from the raw materials used or incorporated into the various reagents used during the process.

Claims

CLAIMS 1. Use of phosphoric acid as a source of phosphate anions for the preparation of so-called primary particles of ferric phosphate (FePO4.xH2O), by coprecipitation with ferrous salts in the presence of a carbon source followed by oxidation, characterized in that it comprises from 0.1 to 400 ppm of at least one of the metallic, respectively metalloid microelements chosen from Na, S, F, Mg, Zn, and K, Cl, Al, Ca, Co, Cr, Fe, K, Mn, Mo, Ni, Ti, V, Cd and As, used alone or in combination.

2. Use according to claim 1, characterized in that said microelements, used alone or in combination, are present in phosphoric acid in quantities as defined in the following table: Microelement conc. (ppm) Microelement conc. (ppm) 3. Use according to claims 1 and 2, characterized in that said microelements present in phosphoric acid are of endogenous or exogenous origin.

4. Use according to claim 3, characterized in that said microelements are of endogenous origin, derived from natural mineral materials or mining waste used as raw material during the preparation of phosphoric acid.

5. Use according to at least one of claims 1 to 4, characterized in that the preparation of the so-called primary particles (FePO4.xH2O) is carried out at a pH between 2.5 and 3.

0.

6. Process for the preparation of particles of lithiated ferric phosphate (LiFePO4) of micrometric size and nanoporous morphology, by lithiation and subsequent calcination of the so-called primary particles (FePO4.xH2O) obtained according to claims 1 to 5.

7. Method according to claim 6, characterized in that the lithiation of the so-called primary particles (FePO4.xH2O) is carried out by solid reaction, i.e. mixing and dry grinding of the reactants, followed by calcination under an inert atmosphere, at a temperature between 550 and 750°C.

8. Method according to claim 6, characterized in that lithiation of the so-called primary particles (FePO4.xH2O) is carried out by mixing the reactants in suspension, followed by atomization at a temperature between 80 and 120°C then calcination under an inert atmosphere, at a temperature between 550 and 750°C.

9. Use of lithium ferric phosphate particles (LiFePO4) of micrometric size and nanoporous morphology as obtained by means of the method according to claims 6 to 8, as cathode material in the manufacture of lithium-ion batteries of high electrochemical performance, in particular with high charge density and conductivity.

0. Cathode material used in the manufacture of high electrochemical performance lithium-ion batteries comprising particles of lithium ferric phosphate (LiFePO4) of micrometric size and morphology structure, as obtained by means of the method according to at least one of claims 6 to 8.

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