HK1096371B - Lithium metal phosphates, method for producing the same and use thereof as electrode material - Google Patents

Description

Lithium metal phosphate, method for the production thereof and use thereof as electrode material

The invention relates to a method for producing lithium iron phosphate, to the resulting materials with a small particle size and a narrow particle size distribution, and to the use thereof, in particular in secondary batteries.

The prior art discloses synthetic lithium iron phosphate (LiFePO)₄) The lithium ion battery can be used as a cathode material. This is described for the first time in volume a.k.padhi, k.s.nanjundaswamy, j.b.goodenough, j.electrochem.soc.144 (1997) and is also disclosed, for example, in US 5910382.

Furthermore, WO 02/099913A1 describes the use of phosphates, such as lithium iron phosphate, as positive electrodes for secondary lithium batteries, in order to obtain lithium from Li⁺、Fe³⁺And PO₄ ^3-Is prepared by evaporating water to obtain a solid mixture, then decomposing the solid mixture at a temperature below 500 ℃ to form pure Li and Fe phosphate precursors, and then obtaining LiFePO by reacting the precursors in a reducing atmosphere at a temperature below 800 ℃ to obtain LiFePO₄And (3) powder.

The prior art also discloses the so-called sintering process. One disadvantage is the high material cost of the starting chemicals (e.g., iron oxalate). The consumption of protective gas during the sintering process is also high and toxic by-products, such as CO, are formed during sintering. It has also been found that the particle size distribution of the product is generally broad and bimodal. For example, WO 02/083555, EP 1094523A1, US2003/0124423 and Franger et al, Journal of Power Sources119-121(2003), pp.252-257 disclose other production methods.

JP 2002-. The method for producing lithium iron phosphate is characterized in that a lithium compound, a ferrous compound and a phosphoric acid compound are mixed so that the molar ratio of at least ferrous ions and phosphoric acid ions is about 1: 1, and the mixture is reacted in a hermetically sealed vessel at a temperature ranging from 100 ℃ to 200 ℃ with the addition of a polar solvent and an inert gas. The lithium iron phosphate thus obtained is then physically pulverized.

Although usable lithium iron phosphate salts can be obtained by the processes of the prior art, the conventional production processes have the disadvantage that it is not possible to obtain powdery lithium iron phosphate salts having very small particle sizes and a very narrow particle size distribution.

Therefore, there is a strong urgent need for a suitable method for preparing lithium iron phosphate having a very small particle size and a very narrow particle size distribution, which can be successfully incorporated into an electrode material for a secondary battery and exhibits very good electrochemical properties.

It is therefore an object of the present invention to provide a process for preparing lithium iron phosphate which avoids the disadvantages of the prior art and in particular provides a material which is particularly suitable for the electrodes of rechargeable batteries.

According to the invention, the above object is achieved by the method of claim 1. The dependent claims provide advantageous or preferred developments.

The method of the invention can be used for preparing LiFePO₄Besides, the method can also be used for preparing the empirical general formula LiMPO₄Wherein M represents at least one metal of the first transition series. Generally, M is at least one metal selected from the group consisting of Fe, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Be, Mg, Ca, Sr, Ba, Al, Zr, and La. It is particularly preferred that M is selected from Fe, Mn, Co and/or Ni. However, preferably M comprises at least Fe.

In the compound LiMPO₄M may also represent two or more transition metals; for example LiFePO₄The iron in (b) may be partially replaced by one or more other metals selected from the above group, for example by Zn. LiFePO is particularly preferred₄. According to the process of the invention, LiMPO₄Preferably in pure phase.

According to the invention, it has surprisingly been found that in a process for preparing LiMPO₄In which at least one Li is incorporated by intensive dispersing or milling treatment⁺Source, at least one m²⁺Source and at least one PO₄ ^3-Precursor mixtures or precursor suspensions of the sources, which lead to the final product LiMPO₄Has a very narrow particle size distribution and a very small particle size.

According to the invention, the precursor mixture is treated by dispersing or milling, with intensive mixing and deagglomeration or comminution of the particle agglomerates in the suspension. This is not achieved by conventional stirring at low speeds.

To achieve the dispersing or milling treatment according to the invention, any apparatus which is deemed suitable by the skilled worker can be used, and sufficient shear forces or vortexes can be generated to achieve intensive mixing and at the same time deagglomeration or comminution of the particle agglomerates in the suspension to a D90 value of less than 50 μm. Preferred apparatus include dispersers (with or without pump rotors), Ultraturrax, mills, such as colloid mills or Manton-Gaulin mills, intensive mixers, centrifugal pumps, in-line mixers, mixing nozzles, such as injection nozzles or ultrasound devices. These devices are known per se to the skilled person. The desired setting can be determined by routine experimentation, depending on the type of apparatus, in order to obtain the desired effect on the average particle size of the precursor suspension (see above).

In most cases, the input power in the precursor suspension is at least 5kW/m for the dispersing or milling treatment according to the invention³The mixture or suspension treated, in particular at least 7kW/m³. The input power can be determined in a known manner by the device, for example by the formula P ═ 2 · pi · n · M, where M denotes torque and n denotes number of revolutions, when an Ultra-Turrax stirrer is used.

According to a further preferred embodiment of the invention, for the dispersing or milling treatment according to the invention, the energy input in the precursor suspension is at least 5kWh/m³The mixture or suspension treated, in particular at least 7kWh/m³. In this case, it is preferable (but not mandatory) to also coincide with the values mentioned above for the input power.

It has also surprisingly been found that, in the production process according to the invention, instead of a dispersing or grinding treatment, the LiMPO produced is used₄Crushing can not lead to LiFePO₄The powders have correspondingly advantageous properties, even if attempts are made to obtain comparable particle size distributions.

Without limiting the invention to this theoretical mechanism, it is believed that the large crystal agglomerates initially formed during the production of the mixed suspension are prevented or at least comminuted after their formation during the dispersing or milling process according to the invention. As an intermediate product, the crystal agglomerates can also be (partly) attributed to Li⁺And M²⁺Depending on their concentration, the phosphates increase viscosity due to the formation of larger crystal platelets or agglomerates. Thus, according to a particularly preferred embodiment of the invention, it is also possible to subject the precursor mixture or suspension to a dispersing treatment using a device whose high mixing action (or shearing action) is sufficient to prevent the formation of large crystals or crystal agglomerates in the mixture or suspension, while at the same time providing a high nucleation rate. Non-limiting examples of suitable devices have been mentioned above.

Said crystal agglomerate orThe crystalline platelets may also be formed by dissolving Li in the solvent⁺Source, soluble M²⁺Source and (soluble) PO₄ ^3-Source precipitation-defined precursor formation. In the following examples of the invention, for example, Fe is added²⁺Aqueous solutions of sources, especially iron (II) sulfate heptahydrate FeSO₄·7H₂Aqueous solution of O, and liquid PO₄ ^3-Source, especially 85% phosphoric acid, and slowly adding aqueous Li⁺The source, especially in the case of aqueous LiOH solution, precipitates iron bluestone (Fe)₃(PO₄)₂Hydrate) was added. Here, it is preferred that the dispersing or milling treatment is carried out already from the start of the initial crystal formation until the end of the precipitation, to prevent the formation of large crystal platelets or crystal agglomerates, or to pulverize them. Before the subsequent, preferably hydrothermal treatment, a homogeneous precursor mixture or suspension is present, preferably containing a mixture comprising vivianite (optionally impregnated with Li), using dispersing or grinding equipment⁺Ions), lithium phosphate and/or iron hydroxide. It is not necessary to isolate the intermediate product. The precursor mixture or suspension is preferably already combined and/or precipitated in the hydrothermal vessel (one-pot process).

The dispersing or milling treatment according to the invention thus ensures a very uniform precipitation and the formation of a homogeneous mixture consisting of a large number of small crystal nuclei of approximately the same size. The crystal nuclei can then react to form the end product LiMPO with a very narrow particle size distribution, in particular during the subsequent hydrothermal treatment₄A very uniformly grown crystal. In principle, it is also possible within the scope of the present invention, instead of the hydrothermal treatment, optionally after separation of the mother liquor (for example by filtration and/or centrifugation), to dry and optionally sinter the precipitate formed from the dispersion-or mill-treated precursor mixture according to the invention. However, hydrothermal treatment is preferred and gives the best results.

To obtain the desired effect, it is also preferred to start the dispersing or milling treatment of the invention before or during the precipitation of the precipitate from the precursor mixture, to prevent the formation of macrocrystalline nuclei or agglomerates, or to pulverize and homogenize them. The D90 value of the particles in suspension was less than 50 μm. It is preferred that the D90 value of the particles in the precursor suspension is at most 25 μm, in particular at most 20 μm, particularly preferably at most 15 μm, since optimum properties of the end product can be observed at these values.

According to one embodiment of the invention, the dispersing or milling treatment according to the invention can also be carried out after precipitation of the precipitate from the precursor mixture, provided that the above-mentioned D90 value is reached.

It has also been surprisingly found that, for best results, the dispersing or milling treatment according to the invention is preferably carried out before the final reaction to form lithium iron phosphate, in particular before the hydrothermal treatment after precipitation of the precursor mixture is complete. However, treatment of the precursor mixture before and during the hydrothermal treatment is also considered to be a dispersing or milling treatment of the present invention.

The method of the invention has the major advantage that the LiMPO produced can be controlled particularly reproducibly₄The particle size distribution of (a) can stably maintain good electrochemical properties without large fluctuation.

In the present invention, Li⁺Source, M²⁺Source and PO₄ ^3-The choice of source is essentially unlimited. All starting materials familiar to the skilled worker or deemed suitable can be used. A wide variety of lithium compounds, divalent compounds of M, and phosphate compounds can be used in appropriate combination as synthesis raw materials. Preferably soluble salts or compounds of Li and M and liquid or soluble PO₄A source. Examples of suitable lithium compounds are, without limitation, in particular lithium fluoride, lithium chloride, lithium bromide, lithium iodide, lithium carbonate, lithium hydroxide or lithium phosphate. LiOH is particularly preferred.

Examples of divalent compounds of M, such as M ═ Fe, are in particular, but without limitation, iron fluoride, iron chloride, iron bromide, iron iodide, iron sulfate, iron phosphate, iron nitrate, organic salts of iron, such as iron oxalate or iron acetate. Iron sulfate is particularly preferred. If M is a metal other than Fe, a similar compound may be used.

Examples of phosphoric acid compounds are, without limitation, in particular orthophosphoric acid, metaphosphoric acid, pyrophosphoric acid, triphosphoric acid, tetraphosphoric acid, hydrogen or dihydrogen phosphate, such as ammonium or dihydrogen phosphate, lithium or iron phosphate, or any mixtures thereof. Phosphoric acid is particularly preferred.

Furthermore, when LiOH is used as Li⁺Source and phosphoric acid as PO₄ ^3-The source, the phosphoric acid may be neutralized by adding LiOH to initiate precipitation in the precursor mixture.

According to the invention, at least one Li is contained⁺Source, at least one M²⁺Source and at least one PO₄ ^3-Any liquid or fluid mixture of sources may be considered a precursor mixture.

According to the invention, any liquid or fluid precursor mixture after at least partial precipitation of a precipitate can be considered as a precursor suspension. The precipitate may contain LiMPO₄Or an intermediate product.

Typically, the precursor mixture contains a solvent, especially a polar solvent. As polar solvents, mention may be made, for example, of water, methanol, ethanol, 2-propanol, ethylene glycol, propylene glycol, acetone, cyclohexanone, 2-methylpyrrolidone, ethyl methyl ketone, 2-ethoxyethanol, propylene carbonate, ethylene carbonate, dimethyl carbonate, dimethylformamide or dimethyl sulfoxide, or mixtures thereof. Water is preferred as the solvent. The wet precipitation of LiMPO from aqueous solutions preferred according to the invention can be carried out₄. According to the invention, it is also possible to prepare LiMPO starting from known starting materials or solutions or suspensions familiar to the skilled worker₄. In particular, the formulations and methods known for wet precipitation from solutions can be used, wherein the dispersing or milling treatment according to the invention is additionally carried out. In preparing a precursor mixture or combining at least one Li⁺Source, at least one M²⁺Source and/or at least one PO₄ ^3-In the process of the source, the temperature is preferably about 20-80 ℃, especially 25 ℃ -60℃。

According to a preferred embodiment of the process according to the invention, the precursor mixture or precursor suspension is not directly evaporated or dried. According to a preferred embodiment, it is also possible not to sinter the precursor mixture or precursor suspension, since this has a negative effect on the properties of the resulting end product.

Furthermore, it has surprisingly been found that the fully reacted LiFePO can be obtained by hydrothermal treatment of the precursor mixture or precursor suspension and subsequent drying and optionally sintering₄The best results are obtained.

Within the scope of the present invention, conversion of the precursor mixture under hydrothermal conditions means any treatment at a temperature above room temperature and a vapor pressure above 1 bar. The hydrothermal treatment is carried out in a manner familiar and known to the skilled person. The hydrothermal conditions preferably employ a temperature of 100 to 250 ℃, especially 100 to 180 ℃, and a pressure of 1 bar to 40 bar, especially 1 bar to 10 bar, vapor pressure. Possible hydrothermal processes are described, for example, in JP 2002-. According to one embodiment, the precursor mixture is reacted in a hermetically closed or pressure-resistant vessel. The reaction is preferably carried out in an inert gas or protective gas atmosphere. Suitable inert gases are, for example, nitrogen, argon, carbon dioxide, carbon monoxide or mixtures thereof. The hydrothermal treatment may be carried out, for example, for 0.5 to 15 hours, particularly 3 to 11 hours. By way of non-limiting example only, the following specific conditions may be selected: heating from 50 deg.C (temperature of precursor mixture) to 160 deg.C for 1.5 hr, hydrothermal treating at 160 deg.C for 10 hr, and cooling from 160 deg.C to 30 deg.C for 3 hr.

According to a preferred embodiment of the invention, M is first mixed in an aqueous medium, in particular under an inert gas atmosphere²⁺Source and PO₄ ^3-Source, then Li is added again, preferably under an inert gas atmosphere⁺A source. Finally, as the neutralization of the precursor mixture increases to initiate precipitation, the dispersion or milling process then begins and the reaction proceeds under hydrothermal conditions. An embodiment according to the inventionBy way of example, the LiMPO is separated from the suspension after hydrothermal treatment₄For example by filtration and/or centrifugation. Furthermore, according to one embodiment of the invention, the separated LiMPO is washed₄In particular with water, in order to reduce or remove the salt content. Likewise, LiMPO may be treated after hydrothermal treatment₄Drying and/or sintering is carried out, in particular in a protective gas or inert gas atmosphere. Careful drying/redrying is generally required for the electrochemical quality of the end product, since even small traces of moisture can cause problems for the material in the electrochemical application of Li accumulators or Li cells, for example by making the conductive salt LiPF₆And (5) decomposing. Optionally, sintering may be performed.

Can be used for LiMPO in a wide temperature range of about 50 to 750 DEG C₄Drying is carried out at a temperature which also depends on economic considerations. If the LiMPO is prepared in the absence of carbon-containing or electrically conductive substances or precursors thereof (see below)₄In many cases, drying at about 50 to 350 ℃, for example, at 250 ℃ for 3 hours, and drying using nitrogen gas 5.0, vacuum or synthesis gas (Formiergas) is sufficient.

If the LiMPO is prepared in the presence of a carbon-containing or electrically conductive substance or a precursor thereof (see below)₄To act as a precoating carbon, a higher drying temperature is generally selected, typically above 500 or 700 ℃. In particular, the sintering may be carried out, for example, by heating at about 750 ℃ for 3 hours using 5.0 g of nitrogen. Only at sufficiently high temperatures, the desired electrically conductive coating of the carbon-containing or electrically conductive substance can be obtained.

According to a preferred embodiment of the invention, the components of the precursor mixture have the following stoichiometric proportions:

a.1mol Fe²⁺∶1mol PO₄ ^3-∶1mol Li*(1∶1∶1)

b.1mol Fe²⁺∶1mol PO₄ ^3-∶3mol Li*(1∶1∶3)

c.a and b in any mixing ratio

Preferably M²⁺Iron ion and PO₄ ^3-Is at least about 1: 1. The above stoichiometric proportions are also preferred from an economic point of view, but are not mandatory. In the hydrothermal process, LiMPO₄Preferably already formed as the thermodynamically most stable phase and, furthermore, deviations from the above-mentioned proportions to influence precipitation or morphological properties may even be deliberate in individual cases. Deviations from the abovementioned stoichiometric proportions of even 20%, at least about 10%, can generally be tolerated.

Hydrothermal processes also have the advantage of greatly reducing the protective gas requirements compared to alternative sintering processes from dry powder premixes or precursor mixtures. Furthermore, it has surprisingly been found that the particle morphology and particle size distribution can be controlled more precisely than with a pure sintering process.

Too large a LiFePO at high charge-discharge rates (high charge-/discharge currents)₄The particles lead to a kinetically controlled limitation of the capacity that can be removed from the battery (entnembar), i.e. lithium ions can no longer rapidly migrate through the interfacial layer LiFePO during discharge₄/FePO₄The specific capacity of the electrode drops significantly at high charge/discharge rates. However, for commercial lithium iron phosphate, a sufficient specific capacity is important even at high charge/discharge currents.

The studies carried out by the inventors have also shown that LiMPO is obtained by simple regrinding and/or screening of the final LiMPO which has not been subjected to the dispersing or milling treatment according to the invention₄The same small particle size and narrow particle size distribution cannot be achieved, and outstanding electrochemical properties cannot be obtained. LiMPO produced solely by direct sintering of powder precursor mixtures₄As well as so. It is believed that this is due to the uniform and small crystal nuclei which are generated by the dispersing or milling treatment according to the invention and which form the reaction to the finished LiMPO₄The basis of the product. The finely divided and uniform particle size thus obtained for the LiMPO prepared by the process according to the invention₄In the case of drying or sinteringThere is also a positive effect.

Thus, a further aspect of the invention relates to LiMPO obtainable by the process described above₄. Particles D of the material₉₀The value is preferably at most 25 μm, in particular at most 20 μm, particularly preferably at most 15 μm. The average particle diameter (D50 value) is less than 0.8. mu.m, preferably less than 0.7. mu.m, in particular less than 0.6. mu.m, particularly preferably less than 0.5. mu.m. The particle size distribution is preferably at least substantially normal (monomodal). According to one embodiment, the D10 value is less than 0.35. mu.m, preferably less than 0.40. mu.m, but, depending on the D90 value, it can also be higher in the case of narrow particle size distributions. The D90 value is preferably less than 3.0. mu.m, preferably less than 2.5. mu.m, in particular less than 2.0. mu.m.

As described above, the LiMPO of the present invention₄Preferably narrow, and according to a particularly preferred embodiment the difference between the D90 value and the D10 value is not more than 2 μm, preferably not more than 1.5. mu.m, in particular not more than 1 μm, particularly preferably not more than 0.5. mu.m.

Surprisingly, it has been shown that the LiMPO according to the invention₄The above-mentioned advantages of (a) also bring about particular advantages when subsequently treated with other components, for example carbon-containing materials in the preparation of electrode materials. LiMPO of the present invention₄It is clear that it can be better and more easily processed into electrode materials due to its particular particle size distribution (as defined herein) and is particularly intimately associated with, for example, a carbon-containing conductive material. Accordingly, in a further aspect the present invention relates to a composition comprising LiMPO as defined herein₄Especially an electrode material.

Another aspect of the invention relates to LiMPO as defined above₄Use of the material as an electrode material in a lithium battery or a secondary (rechargeable) Li battery. Final LiMPO₄The primary particles (crystalline) of the product are preferably substantially uniform in size and morphology in the REM image. In contrast, LiMPO which is not prepared by the process according to the invention₄Primary particles of non-uniform size or non-uniform crystal morphology.

According to a preferred embodiment of the invention, the preparation or precipitation of the precursor mixture and/or the reaction under hydrothermal conditions is carried out in the presence of further constituents, in particular electrically conductive substances. Preferably, this may be a carbonaceous solid, such as carbon, in particular electrically conductive graphite (Leitkohle) or carbon fibers. It is also possible to use precursors of electrically conductive substances or carbon-containing solids, which precursors are dried or sintered LiMPO₄In the process, into carbon particles, such as sugar compounds. Further examples of suitable organic compounds are described in WO 02/083555, the disclosure of which is incorporated herein by reference. Final LiMPO₄The carbon particles contained in the product are preferably uniformly distributed. According to a particularly preferred embodiment of the invention, the carbon-containing solids used are used as nuclei in the reaction of the precursor mixture.

In principle, however, any method familiar to the skilled person is suitable for introducing carbon or carbon-containing electrically conductive material or mixing with other components. It is also possible to use the final LiMPO₄Is intensively mixed or milled with at least one carbon-containing solid, such as electrically conductive graphite. Other possible methods include aggregation of the carbon particles to LiMPO in aqueous or nonaqueous suspension₄On the surface of the particles, or pyrolyzed from LiMPO₄A mixture of powder and carbon precursor material. With LiMPO₄The carbon-containing LiMPO thus obtained₄For example, it usually contains up to 10% by weight, preferably up to 5% by weight, particularly preferably up to 2.5% by weight, of carbon.

Industrially, preference is given to a pyrolysis process in which at least one carbon precursor material, preferably a carbohydrate, for example a sugar or cellulose, particularly preferably lactose, is reacted with the LiMPO of the invention₄The powders are mixed, for example kneaded, wherein water may be added as an auxiliary. According to an industrially particularly preferred embodiment, the carbon precursor material is added to the as yet undried, moist LiMPO₄And (3) filtering a cake. Subsequently, the inventive LiMPO₄The mixture of powder and carbon precursor material is dried under a protective gas, in air or in vacuum, at a temperature preferably between 50 ℃ and 200 ℃, and under a protective gas such as nitrogen 50 or argon to a temperature of, for example, 500 to 1000 c, preferably 700 to 800 c, during which the carbon precursor material is pyrolysed to form carbon. Followed by a milling or deagglomeration treatment.

According to a further preferred embodiment of the invention, the LiMPO used is determined in accordance with DIN 66131 (multipoint determination)₄BET surface area of greater than about 3.5m²A/g, in particular greater than about 4m²A specific preference of more than 5m²A/g of more than 10m²A/g, or even more than 15m²/g。

Improving LiFePO by carbon precoating₄Methods of the nature are also described in: ravet et al, Abstract number 127, 196^thECS-Meeting, Honolulu, H1, 8 months 17-22 (1999).

The carbon content also improves LiMPO by modifying the surface properties₄The powder is processed for processability into a battery electrode and/or to improve electrical connection in a battery electrode.

Alternatively, by purposefully doping Mg²⁺、Al³⁺、Ti⁴⁺、Zr⁴⁺、Nb⁵⁺、W⁶⁺But also significantly improve conductivity (s.y.chung, j.t.bloking, y.m.chiang, Nature, volume 1, august 2002, 123).

Another aspect of the invention relates to a process for the preparation of a LiMPO containing the carbon-containing substances according to the invention₄The Li secondary battery or the Li secondary battery of (1). The secondary battery (lithium ion secondary battery) itself can be produced in a known manner, for example as described below and described in JP 2002-151082. In this case, the lithium iron phosphate of the present invention obtained as above is used as at least a part of the material of the positive electrode of the secondary battery. In this case, according to a general method for preparing a positive electrode of a secondary battery, first, the lithium iron phosphate of the present invention is mixed with a conductive additive and a binder, if necessary. Then, from the positive electrode and the commonly used negative electrode material, such as metallic lithium or a layered carbon compound, such as graphite, and further from the commonly used non-aqueous electrolyte, such as propylene carbonate or ethylene carbonateEsters, etc., in which lithium salts such as LiBF are dissolved₄Or LIPF₆A secondary battery was prepared as a main component.

Measurement of particle size distribution:

determination of the precursor suspension and of the LiMPO produced by light scattering using commercially available equipment₄The particle size distribution of (1). The process is known to the skilled worker, reference being made here also to the disclosure of JP 2002-151082 and WO 02/083555, and incorporated herein by reference. At this point, the particle size distribution was determined with the aid of a laser diffraction measuring apparatus (auf Mastersizer S, german Malvern Instruments GmbH, Herrenberg, DE) and the manufacturer' S software (version 2.19) with a Malvern small volume sample dispersion unit DIF 2002 as measuring unit. The following measurement conditions were selected: compressing the range; the active ray length is 2.4 mm; measurement range: 300 RF; 0.05 to 900 μm. Sample preparation and measurements were performed according to the manufacturer's instructions.

The D90 value represents the value where 90% of the particles in the measured sample have a smaller or equal particle diameter. Accordingly, the D50 value or D10 value represents the value where 50% or 10% of the particles in the measured sample have smaller or equal particle diameters.

According to a particularly preferred embodiment of the invention, the values mentioned in the present description for the D10 value, the D50 value, the D90 value and the difference between the D90 and D10 values are based on the volume fraction of the respective particles in the total volume. Thus, according to this embodiment of the invention, the values D10, D50 and D90 described herein represent values where 10 volume% or 50 volume% or 90 volume% of the particles in the measured sample have smaller or equal particle diameters. With these values being maintained, particularly advantageous materials can be provided according to the invention, and the negative influence of relatively large particles (relatively large volume fractions) on the processability and the electrochemical product properties can be avoided. The values mentioned in this specification for the D10 value, the D50 value, the D90 value and the difference between the D90 and D10 values are also particularly preferably in percent or volume percent of the particles.

In addition to LiMPO₄In the case of compositions which also contain other constituents (for example electrode materials), in particular carbon-containing compositions, the light scattering method described above leads to misleading results, since LiMPO₄The particles may be combined with additional (e.g., carbonaceous) material into larger agglomerates. However, in such compositions LiMPO₄The particle size distribution of (c) can be determined by REM imaging as follows:

a small sample of the powder was suspended in acetone and dispersed with ultrasound for 10 minutes. A few drops of the suspension were then immediately dropped onto a sample slide of a scanning electron microscope (REM). The solids concentration and the number of drops of the suspension are metered such that a substantially monolayer of powder particles (the term "particles" is used as a synonym for "particles") is formed on the slide to prevent the powder particles from hiding from each other. The drop must be made quickly before the particles can be separated by settling to size. After air drying, the sample was transferred to the measurement chamber of REM. In this example, the REM is an LEO 1530 type apparatus, operating with a field emission electrode at 1.5kV excitation voltage and a sample spacing of 4 mm. At least 20 cross-sectional enlargements of randomly determined magnification 20000 are taken from the sample. They were each printed on DIN a4 paper with an inserted magnification scale. At least 10 freely visible LiMPOs were randomly selected, if possible, on each of at least 20 sheets₄Particles from which powder particles are formed together with a carbonaceous material, LiMPO₄The boundaries of the grains are determined by the absence of directly grown bridges of solids. However, the bridges formed by the carbon material are considered to belong to the grain boundaries. For each of these selected LiMPOs₄Particles, the longest and shortest axes of the projection are measured with a ruler, respectively, and converted to true particle size based on the scale. For each measured LiMPO₄The particle diameter is defined as the arithmetic mean of the longest and shortest axes. Then, similarly to the case of using light scattering measurement, the measured LiMPO was measured₄The particles are classified into size classes. If the respective associated LiMPOs are plotted against the size scale₄The number of particles, a particle size distribution based on the differentiation of the number of particles is obtained. If the number of particles is continuously added from small particle grade to large particle gradeA cumulative particle size distribution is obtained, whereby D10, D50, and D90 can be read directly on the size axis.

The process is also useful for LiMPO-containing compositions₄The battery electrode of (1). In this case, however, instead of a powder sample, a new cut or broken surface of the electrode is fixed to the specimen slide and studied under REM.

The invention will now be explained in more detail by means of the following non-limiting examples. The attached drawings are as follows:

FIG. 1 shows LiMPO prepared according to the invention in example 1₄Particle size distribution (by volume);

FIG. 2 shows LiMPO prepared according to the invention in example 2₄Particle size distribution (by volume);

FIG. 3 shows LiMPO prepared according to the invention in example 3₄Particle size distribution (by volume).

Example (b):

example 1: according to the method of the invention, LiFePO is prepared by hydrothermal treatment ₄

Reaction type

FeSO₄·7H₂O+H₃PO₄+3LiOH·H₂O→LiFePO₄+Li₂SO₄+11H₂O

LiFePO₄The final product can be stored in air at room temperature without oxidation.

Preparation of LiFePO according to the reaction scheme shown₄It is noted that LiFe^IIPO₄From Fe^IIThe precursor precipitates out of the aqueous solution. Thus, the reaction and drying/sintering are carried out under protective gas or in vacuum,to avoid Fe^IIPartial oxidation to Fe^IIIFormation of by-products such as Fe₂O₃Or FePO₄。

Preparation and precipitation of precursor mixtures

417.04g FeSO₄·7H₂O was dissolved in about 1 liter of distilled water, and 172.74g of 85% phosphoric acid was slowly added with stirring. Then, 1.5 liters was added with distilled water. The acidic solution was charged to a laboratory autoclave (volume: 1 gallon) at a stirrer speed of 400UPM, nitrogen gas was passed through a submerged tube into the autoclave at about 6-7 bar, and then the pressure was again relieved via an evacuation valve. This process was repeated 2 times.

188.82g lithium hydroxide LiOH H₂O was dissolved in 1 liter of distilled water.

For the dispersing or milling treatment according to the invention, a disperser (Firma IKA,UTL 25 basiclinline with a dispersion chamber DK 25.11). The pumping direction of the disperser was bottom outlet valve-disperser-purge valve. The disperser started at an average power level (13500UPM) as specified by the manufacturer.

The prepared LiOH solution is then pumped into the autoclave by means of a production membrane pump via a submerged tube (stroke 100%, 180 strokes/min; corresponding to the maximum power of the pump) and then rinsed with about 500 to 600ml of distilled water. The process lasts about 20 minutes, during which the temperature of the respective suspension is raised to about 35 ℃. After pumping and flushing, the suspension was heated to 50 ℃ in an autoclave. A dark green precipitate precipitated after the addition of lithium hydroxide.

The disperser started before the start of the addition of LiOH was used for a total of about 1 hour to intensively mix or grind the very viscous suspension formed (after pumping the LiOH solution at 50 ℃). The particle size was then 13.2 μm, when the particle size was D90. The values of D90 by volume are similar.

To measure the particle size in the precursor suspension, one can proceed as follows: referring to the method for measuring particle size (distribution) given before the example, 20 to 40mg of the suspension were suspended in 15ml of water and dispersed with an ultrasonic probe (25 watts net power, 60% power) for 5 minutes. The measurement is then carried out immediately in the measuring unit. The correct setting of the sample quantity in each case can be checked by a display on the measuring device (green measuring range).

The use of a disperser serves to intensively mix and deagglomerate the precipitated viscous premix. During the precipitation and crystallization of the precursor suspension, the preliminary grinding or intensive mixing in the disperser results in a homogeneous mixture of a large number of small crystal nuclei of approximately the same size. The crystal nuclei are crystallized in a subsequent hydrothermal treatment (see below) to form the very uniformly growing end product LiFePO₄The crystal of (4) has a very narrow particle size distribution. The power or energy input of the dispersion treatment is respectively more than 7kW/m³Or greater than 7kWh/m³Treated precursor mixture/suspension.

Hydrothermal treatment:

each freshly prepared suspension was hydrothermally treated in a laboratory autoclave. Before heating the suspension, the autoclave was purged with nitrogen in order to remove the air present from the autoclave before the hydrothermal treatment. Formation of LiFePO starting from hydrothermal temperatures of about 100 to 120 ℃₄. After the hydrothermal process, the material was filtered with a Seitz filter and washed. The method comprises the following specific steps:

after the disperser was turned off and disconnected, the batch was heated to 160 ℃ over 1.5 hours and subjected to hydrothermal treatment at 160 ℃ for 10 hours. Then cooled to 30 ℃ over 3 hours.

Then LiFePO₄Drying in air or in a drying oven, for example at mild temperatures (40 ℃), does not result in significant oxidation.

However, the material obtained as described above may also be subjected to the following further treatments:

filtration of lithium iron phosphate LiFePO₄

After the hydrothermal treatment, the cooled suspension (up to 30 ℃) was pumped under nitrogen through the bottom outlet valve of the autoclave into a pressure filter (the so-called "Seitz filter"). The production membrane pump is adjusted in such a way that the pressure does not exceed 5 bar. The filter cake was washed with distilled water until the conductivity of the wash water was less than 200. mu.S/cm.

Drying and deagglomerating lithium iron phosphate LiFePO₄

The filter cake was pre-dried overnight in a vacuum oven at 70 ℃ to a residual moisture of less than 5%, and then in a protective gas oven ("Linn KS 80-S") at 2001/h of a synthesis gas stream (90% N)₂ /10％H₂) Next, the mixture was dried again at 250 ℃ until the residual moisture was < 0.5%. The LiFePO was then subjected to a laboratory rotor mill ("Fritsch Pulverisette 14") with a 0.08mm sieve₄And (4) deagglomerating.

The final LiFePO can be seen from FIG. 1₄(treatment with disperser, hydrothermal treatment followed by drying and deagglomeration as described above). In order to illustrate the advantageous particle size distribution and the absence of interfering larger particles in the product according to the invention, the data are shown on a volume basis. The values in terms of particle content (%) are as follows: d50 value less than 0.5 μm; d10 value less than 0.35 μm; d90 value less than 2.0 μm; the difference between the D90 value and the D10 value was less than 1.5 μm.

To measure the particle size of the powdery sample, the following can be done: the particle size (distribution) was determined as given before in the reference example, 20 to 40mg of the powder sample were suspended in 15ml of water and dispersed for 5 minutes with an ultrasonic probe (25 watts net power, 60% power). The measurement is then carried out immediately in the measuring unit. The correct setting of the sample quantity in each case can be checked by a display on the measuring device (green measuring range).

Example 2: preparation of LiFePO₄Without disperser treatment (comparative)

For comparison, LiFePO was prepared according to the same synthesis as described in example 1₄However, no disperser is used according to the invention. Under otherwise identical reaction conditions, a distinctly broader particle size distribution is obtained, with a greater proportion of agglomerate structures growing. D after addition of LiOH solution without using a disperser₉₀The value (in volume content or particle count) is greater than 200 μm. FIG. 2 shows that, although a pure-phase LiFePO is likewise obtained₄But finally LiFePO₄The particle size distribution of (b) is significantly coarser (after hydrothermal treatment, drying and deagglomeration). To illustrate the presence of interfering larger particles, the data is presented in volume. The D50 value in terms of particle content (%) exceeded 0.8. mu.m.

According to US2003/0124423, page 10, [0015 ]]LiFePO produced by the process₄The particle size distribution of the product of the invention cannot be achieved despite intensive grinding with a pestle; a D50 value of less than 0.8 μm and a difference between D90 and D10 values of 2 μm or less cannot be obtained.

Example 3: according to the method of the invention, LiFePO is prepared by hydrothermal treatment₄

LiFePO was prepared according to the same synthesis as described in example 1₄However, the disperser (Firma IKA, ULTRATURRAXAGO) is operated at the highest power level^_UTL 25 basiclinline with a dispersion chamber DK 25.11). The power or energy input of the dispersion treatment is more than 10kW/m³Or more than 10kWh/m³Treated precursor mixture/suspension. The particle size of the suspension treated by the disperser is D₉₀10.8 μm. The value of D90 by volume is slightly lower than this value.

Hydrothermal treatment, filtration, drying and deagglomeration were carried out as indicated in example 1. The resulting final LiFePO can be seen from FIG. 3₄Typical particle size distribution. For the purpose of illustrationThe favorable particle size distribution and the absence of interfering larger particles in the product according to the invention represent the data on a volume basis. The values in terms of particle content (%) are as follows: d50 value less than 0.5 μm; d10 value less than 0.35 μm; d90 value less than 2.0 μm; the difference between the D90 value and the D10 value was less than 1.0 μm.

In electrochemical tests, the LiFePO of the invention produced using a disperser compared with comparative materials produced without using a disperser and materials produced according to the prior art by a simple sintering process₄Exhibit optimum properties, especially at high charge/discharge rates.

Example 4: according to the method of the invention, LiFePO is prepared by hydrothermal treatment₄

21.894kg FeSO₄*7H₂O was dissolved in 42 liters of deionized water and 9.080kg of 85% phosphoric acid was added slowly with stirring. The acidic solution was charged to a glazed 200 liter autoclave with an anchor stirrer and stirred at 45 UPM. The top of the autoclave was purged with nitrogen before closing. The acidic solution was circulated through a centrifugal pump, which consumed about 5kW of power and had a measured average flow of 7000 litres per hour. The solution was discharged through the bottom outlet valve of the autoclave and was added again through the top flange. 10.289kg LiOH H₂O was dissolved in 62 liters of deionized water. The alkaline solution is fed to the circulating acidic solution at the pressure side of the centrifugal pump by means of a single-screw pump and an injection nozzle. This process continued for 15 minutes, with the temperature of the circulating solution increasing from 18.3 ℃ to 42.1 ℃. The suspension thus formed was recirculated for 45 minutes by means of a centrifugal pump and stirred with an anchor stirrer at 45UPM, during which the temperature was raised again to 51.1 ℃. According to the invention, the centrifugal pump ensures the formation of a suspension of fine particles with its high swirling action throughout the process, whereby a particle size distribution comparable to that of example 1 can be achieved. The power or energy input treated by the disperser is more than 7kW/m³Or more than 7kWh/m³Treated precursor mixture/suspension.

After the external equipment was closed and disconnected, the autoclave was sealed gas-tight and heated to 160 ℃ over 1.5 hours with constant stirring at 90UPM, and the temperature was maintained for 10 hours. The final LiFePO was then cooled to 20 ℃ in 3 hours, analogously to example 1, filtered in a "Seitz filter₄A suspension. The pH of the filtrate was 7.5. Then washed with deionized water until the filtrate had a conductivity value of less than 480. mu.S. The off-white, solid and readily soluble filter cake was dried overnight at 70 ℃ in a vacuum drying oven < 100mbar and deagglomerated in a laboratory rotor mill ("Fritsch Pulverisette 14") with a 0.08mm sieve. The particle size distribution thus obtained had the same range as in example 1.

Example 5: carbonization of materials produced according to the method of the invention

1kg of dried LiFePO obtained in examples 1 to 4₄The powder was thoroughly mixed with 112g of lactose monohydrate and 330g of deionized water and dried overnight at 70 ℃ in a vacuum drying cabinet at < 100mbar to a residual moisture of < 5%. The brittle hard dry product was broken off by hand and coarsely ground in a disk mill ("Fritsch Pulverisette 13") with a disk spacing of 1mm and then transferred into a stainless steel crucible of a protective gas chamber oven ("Linn KS 80-S"). The mixture was heated to 750 ℃ over 3 hours under a stream of 200 l/h of nitrogen, maintained at this temperature for 5 hours and cooled to room temperature over about 36 hours. The carbonaceous product was deagglomerated in a laboratory rotary mill ("FritschPulverisette 14") with a 0.08mm screen.

REM analysis of the particle size distribution was performed as described for the carbonaceous material before the examples, yielding the following values: the D50 value was less than 0.6 μm and the difference between the D90 value and the D10 value was less than 1.5 μm.

In electrochemical tests on thin-film electrodes, as disclosed, for example, in Anderson et al, electrochem. and Solid State Letters 3(2) (2000), pages 66-68, the inventive materials containing carbon (starting from the products of examples 1, 3 and 4) exhibit the best properties, especially at high charge/discharge rates, compared to comparative materials prepared without using dispersers and to materials prepared according to the prior art by a simple sintering process.

Claims (42)

1. Preparation of LiMPO of the formula₄A method of compound, wherein M represents at least one metal of a first transition series, comprising the steps of:

a. preparation of a catalyst containing at least one Li⁺Source, at least one M²⁺Source and at least one PO₄ ^3-A precursor mixture of the source to precipitate out a precipitate to produce a precursor suspension;

b. dispersing or milling the precursor mixture and/or precursor suspension until the particles in the precursor suspension have a D90 value of less than 50 μm;

c. obtaining LiMPO from the precursor suspension obtained according to b) by reaction under hydrothermal conditions₄。

2. A method according to claim 1, characterized in that the particles in the suspension have a D90 value of at most 25 μm.

3. Method according to claim 1 or 2, characterized in that M comprises at least Fe or is Fe.

4. A method according to one of the preceding claims 1 to 3, characterized in that M comprises Fe, Mn, Co and/or Ni.

5. A process according to one of the preceding claims 1 to 3, characterized in that the LiMPO is obtained in phase-pure form₄。

6. A method according to one of the preceding claims 1 to 3, characterized in that a dispersing or milling treatment is used before or during the precipitation of the precursor mixture and is continued until the end of the precipitation.

7. A method according to one of the preceding claims 1 to 3, characterized in that a dispersing treatment is used before the precipitation of the precursor mixture in order to ensure a large number of nucleation and to prevent the formation of large crystals and crystal agglomerates.

8. A process according to one of the preceding claims 2 or 3, characterized in that no evaporation is carried out before the precursor mixture or suspension is reacted under hydrothermal conditions.

9. A method according to one of the preceding claims 2 or 3, characterized in that no sintering is carried out before the precursor mixture or suspension is reacted under hydrothermal conditions.

10. Process according to one of the preceding claims 2 or 3, characterized in that the LiMPO is dried after the reaction under hydrothermal conditions₄。

11. A method according to one of the preceding claims 1 to 3, characterized in that the preparation of the precursor mixture or suspension or the reaction under hydrothermal conditions is carried out in the presence of at least one further component, and the further component is a carbonaceous substance or an electrically conductive substance or a precursor of an electrically conductive substance.

12. The method of claim 11, wherein the conductive substance is carbon.

13. The method of claim 11, wherein the precursor of the conductive substance is a carbonaceous substance.

14. Process according to one of the preceding claims 1 to 3, characterized in that LiOH or Li is used₂CO₃As a lithium source.

15. Method according to one of the preceding claims 1 to 3, characterized in that Fe is used²⁺Salts as Fe²⁺A source.

16. Process according to one of the preceding claims 1 to 3, characterized in that phosphoric acid, metal phosphate, hydrogen phosphate or dihydrogen phosphate is used as PO₄ ^3-A source.

17. A process according to one of the preceding claims 1 to 3, characterized in that water is used as solvent in the precursor mixture.

18. Process according to one of the preceding claims 1 to 3, characterized in that Li is used in the form of an aqueous solution⁺Source, M²⁺Source of PO in liquid or aqueous form₄ ^3-A source.

19. Process according to one of the preceding claims 1 to 3, characterized in that the precipitate formed in the precursor suspension contains at least one LiMPO₄And then reacted under hydrothermal conditions to form LiMPO₄。

20. The process according to one of the preceding claims 1 or 2, characterized in that temperatures of 100 to 250 ℃ and pressures of 1 bar to 40 bar vapour pressure are used under hydrothermal conditions.

21. A method according to one of the preceding claims 1 to 3, characterized in that the components of the precursor mixture are present in the following stoichiometric ratios:

a.1mol Fe²⁺∶1mol PO₄ ^3-∶1mol Li^*(1∶1∶1)

b.1mol Fe²⁺∶1mol PO₄ ^3-∶3mol Li^*(1∶1∶3)

c. any mixing ratio between a and b.

22. Method according to one of the preceding claims 1 or 2, characterized in that the combination or reaction of the precursor mixture or suspension under hydrothermal conditions is carried out in an inert gas atmosphere.

23. A process according to one of the preceding claims 1 to 3, characterized in that M is first mixed in an aqueous solvent²⁺Source and PO₄ ^3-Source, then, add Li⁺The source, and then the reaction is carried out under hydrothermal conditions.

24. A method according to one of the preceding claims 1 to 3, characterized in that the dispersing or milling treatment is a treatment with a disperser, a mill, an intensive mixer, a centrifugal pump, an in-line mixer, a mixing nozzle, or an ultrasonic device.

25. The process according to claim 24, characterized in that the disperser is an Ultraturrax.

26. A method according to one of the preceding claims 1 to 3, characterized in that for the dispersing or grinding treatment in step b of claim 1, a stirring device is used.

27. A method according to one of the preceding claims 1 to 3, characterized in that a carbon-containing or electrically conductive substance or a precursor of an electrically conductive substance is used as a nucleus in the precipitation or reaction of the precursor mixture.

28. Method according to one of claims 1 to 2, characterized in that LiMPO is separated off after the hydrothermal treatment₄Optionally dried and optionally deagglomerated.

29. Process according to one of claims 1 to 2, characterized in that the LiMPO obtained by hydrothermal treatment₄In a pyrolysis process, wherein at least one carbon precursor material is reacted with LiMPO₄Mixing, wherein water is optionally added as an auxiliary.

30. The method according to claim 29, characterized in that the carbon precursor material is added to the moist LiMPO obtained by separation after hydrothermal synthesis₄In the filter cake, drying by LiMPO₄And a carbon precursor material and heated to a temperature of from 500 ℃ to 1000 ℃, wherein the carbon precursor material pyrolyzes to form carbon.

31. The process of claim 30, wherein the pyrolysis is followed by a milling or deagglomeration process.

32. Method according to claim 30 or 31, characterized in that drying is carried out and pyrolysis is carried out under protective gas.

33. LiMPO obtainable by a process according to one of the preceding claims₄Powder products of LiMPO₄Has an average particle diameter of less than 0.8 [ mu ] m and LiMPO₄The particles have a D10 value of less than 0.4 μm and a D90 value of less than 3.0. mu.m.

34.LiMPO₄Powder product, characterized in that it comprises LiMPO₄Has an average particle diameter of less than 0.8 [ mu ] m and LiMPO₄The particles have a D10 value of less than 0.4 μm and a D90 value of less than 3.0. mu.m.

35. LiMPO according to claim 33 or 34₄A powdered product, characterised in that the difference between the D90 value and the D10 value of the particles is not more than 2 μm.

36. LiMPO according to claim 33 or 34₄Powder product characterized by a BET surface of greater than 3.5m²/g。

37. Composition containing LiMPO according to one of claims 33 to 36₄And (3) powder products.

38. A composition according to claim 37, which is an electrode material.

39. A composition according to claim 37 or 38, further comprising at least one other component which is a carbonaceous or electrically conductive substance or a precursor of an electrically conductive substance.

40. A secondary battery comprising the composition according to claim 38.

41. The secondary battery according to claim 40, wherein the composition is an electrode material.

42. LiMPO according to any of claims 33 to 36₄Use of the powder product as an electrode material.