DE102013206007A1 - Amorphized iron (III) phosphate - Google Patents

Abstract

Process for the preparation of an amorphous or amorphized iron (III) phosphate anhydrate or a carbon composite of amorphous or amorphized iron (III) phosphate anhydrate, characterized in that iron (III) orthophosphate of the general formula FePO4 × 2 H2O or carbon -Composite of iron (III) orthophosphate of the general formula FePO4 × 2 H2O, wherein at least 80% by weight of the iron (III) orthophosphate according to powder X-ray diffraction analysis with CuKα radiation is present in the phosphosiderite (metastrengite II) crystal structure, at a temperature in Range from 140 to 250 ° C down to a residual water content of 0 to 1 wt .-%, which includes both bound crystal water and free water, and dehydrated to a crystal water content ≤ 0.2 H2O.

Description

Subject of the invention

The invention relates to a novel structurally amorphous or amorphized iron (III) phosphate anhydrate and a carbon composite thereof and to a process for the preparation thereof. The structurally amorphous or amorphized iron phosphate anhydrate is suitable for direct use as a cathode material for lithium-ion accumulators as well as a precursor for the production of chemically or thermally lithiated iron phosphate or carbon composite thereof.

The invention further relates to a lithiated iron phosphate and a carbon composite thereof and to a process for its production from the amorphous or amorphized iron (III) phosphate anhydrate or its carbon composite. The product is suitable, among other things, as a cathode material for lithium ion accumulators.

Background of the invention

Rechargeable lithium-ion batteries are widely used energy storage, especially in the field of mobile electronics, since the Li-ion battery is characterized by a high energy density and can deliver a high nominal voltage, so that the lithium-ion battery at comparable power significantly smaller and lighter than conventional accumulators. As cathode materials, spinels such as LiCoO ₂ , LiNiO ₂ , LiNi _1-x Co _x O ₂ and LiMn _n O _{4 have been} established. To increase the safety of Li-ion batteries, especially in terms of thermal overload during operation, LiFePO ₄ was developed as a cathode material. This material is characterized by good performance, high specific capacity and high thermal stability during operation. Iron orthophosphate is a starting material for the production of LiFePO ₄ cathode material for lithium ion accumulators.

High purity requirements are placed on the cathode material of Li-ion accumulators, since any contamination that may undergo unwanted redox reactions during operation (charging and discharging) adversely affects the performance of the accumulator. The type and concentration of the possible contaminations depends essentially on the quality of the raw materials used for the production of the cathode material and their production process per se. In the manufacturing process of the cathode material, measures for the subsequent reduction of impurities can be made, but this is generally associated with an increase in the production costs. It is therefore desirable to use as pure starting materials or raw materials for the production of the cathode material. Besides the purity of the starting materials, their structure and morphology also significantly influence the quality of the cathode material produced therefrom.

The DE 10 2009 001 204 A1 describes the preparation of crystalline iron (III) orthophosphate (FOP) in the form of phosphosiderite crystallites (metastrite II crystallites) with a particular morphology and purity. Due to the special purity and the novel material properties, this iron (III) orthophosphate (FOP) is particularly suitable as a starting material for the production of lithium iron phosphate (LiFePO ₄ , LFP) for lithium-ion batteries, for example according to the US 2010/0065787 A1 described method.

Pure lithium iron phosphate (LFP) has a poor electrical conductivity, which is why it is only partially usable in its pure form as a cathode material. There are therefore various approaches to improve the electrical conductivity of lithium iron phosphate. So describe the US 6,855,273 B2 , the US 2010/0065787 A1 and the DE 10 2011 003 125 For example, the preparation of a carbon coating on the FOP or LFP material to improve the electrical conductivity. The products are also referred to as carbon composite of FOP and LFP and are herein abbreviated to FOP / C and LFP / C, respectively.

The DE 10 2007 049 757 . DE 10 2009 001 204 and DE 10 2011 003 125 describe the preparation of crystalline iron (III) orthophosphate hydrate of the general formula FePO ₄ .nH ₂ O with n ≤ 2.5 or a carbon composite thereof, wherein the iron (III) orthophosphate according to powder X-ray diffraction analysis in the phosphosiderite (Metastrengit II ) Crystal structure is present, which are due to the special manufacturing process and new material properties are excellent as precursors for the production of lithium iron phosphate (LFP) by known methods, for. Example by solid state synthesis by thermal calcination or by hydro and Solvothermalverfahren.

The solid-state synthesis by thermal calcination for the production of LFP or LFP / C has been established in recent years. Compared to hydro- or solvothermal processes, it requires far less apparatus-related effort and is significantly less expensive. The particle size control in the solid state synthesis by thermal calcination, however, is difficult, since process-related high temperatures in the range of 600 to 700 ° C must be used, which can bring a pronounced particle growth and sintering of the calcine with it. Just this should but avoided in the production of LFP in order to keep the diffusion paths for the Li ions short.

The US 2009/0311597 describes the doping of LFP with different transition metals or transition metal compounds to produce cathode materials with acceptable electrical conductivities. The dopants can be distributed homogeneously in the material in the sense of a mixed crystal or be present as a separate crystalline phase in addition to LFP. The doping with transition metals or with lanthanide metals causes high costs for these dopants per se and also requires very expensive and costly process to achieve a conductivity-increasing distribution and doping. The method according to US 2009/0311597 requires very high calcination temperatures of 800 ° C and long calcination times of up to 96 hours, which is a major drawback economically.

Wang et al. (Solid State Ionics, 2007, 178, 843-847) describe a hydrothermal process which yields amorphous iron (III) orthophosphate dihydrate, which is then chemically lithiated in an alcoholic medium at elevated temperature by the addition of ascorbic acid and a lithium salt. The material obtained is amorphous and therefore can not be further characterized. After calcination of this material at 600 ° C for 2 hours under a constant argon flow with 5% hydrogen, an LFP was obtained, which gave at least comparable results in electrochemical half-cell tests over the prior art. That by Wang et al. However, the method described has some disadvantages that preclude a large-scale implementation and thus a commercialization.

Basically, due to the high pressures required, depending on the target temperature and the chosen reaction medium, hydrothermal processes require a complex process design and expensive equipment. Simple, depressurized precipitation reactions, however, have clear advantages.

The amorphous iron (III) orthophosphate dihydrate is prepared according to Wang et al. Although made from inexpensive FeSO ₄ × 7 H ₂ O, this method requires a pH control that can only be achieved by the addition of alkalis. The product therefore inevitably contains contaminations of alkali and / or alkaline earth metal cations and sulfate ions. Wang et al. describe, therefore, that the amorphous iron (III) orthophosphate dihydrate thus prepared must be washed several times in order to sufficiently remove these contaminations of sulfate ions and alkali and / or alkaline earth metal cations.

That from Wang et al. described amorphous iron (III) orthophosphate dihydrate has particle sizes of 100 to 200 nm. The high particle surface therefore offers a large adsorption surface for contaminating anions and cations, with the result that the washing processes have only a low efficiency. In addition, it is described that further dopants in the form of their nitrate salts can be added, which in turn introduces further contamination with nitrate ions into the material.

It is known to those skilled in the art that anionic contaminations in the form of sulfates and / or nitrates in an electrochemical cell result in redox reactions that can exert a corrosive effect on cell components and undesirable interactions with the electrolyte and / or the anode and / or cathode material.

The at Wang et al. described further reaction of amorphous iron (III) orthophosphate dihydrate to LFP in alcoholic medium by addition of ascorbic acid and lithium acetate leads after about 5 hours of reaction at elevated temperature to form an amorphous LFP phase, which can not be further characterized due to the amorphous nature , The large-scale implementation of such a process requires because of the formation of flammable and explosive gas or vapor mixtures of the alcohol of a comprehensive security concept and a high technical equipment cost. Depending on the nature of the alcohol used, such a process is also disadvantageous from an ecological and economical point of view, since the concentrations of the starting materials used are very low due to their low solubility in alcohols with 0.01 mol / liter described and therefore in relation to the product obtained very high amounts of alcoholic reaction medium must be used.

To obtain the crystalline LFP product, it was necessary to calcine hydrogen in argon or nitrogen for at least 2 hours at 600 ° C under a reductive protective atmosphere of 5%. The size and morphology of the primary particles change only insignificantly, but the high temperature inevitably leads to sintering of the primary particles as described in the publication. However, lithium ion diffusion barriers produced by sintering adversely affect the electrochemical quality of the material in lithium-ion secondary batteries. In addition, a porosity is generated in the cathode material, whereby the proportion of active material in the working cathodes of the batteries is reduced. This has a negative effect on the maximum energy density or the maximum amount of active material of the cathodes to be applied.

In further literature ( Masquellier et al., Journal of The Electrochemical Society, 149 (8) A1037-A1044, 2002 ; Hong et al., J. Mater. Chem., 2002, 12, 1870-1874 ; Prosini et al., Journal of The Electrochemical Society, 149 (3) A297-A301, 2002 , it is described that amorphous Fe-PO ₄ × nH ₂ O (n = 0 to 4) can be used directly as a cathode material by electrochemical lithiation in electrochemical cells. The investigated iron phosphate materials were either commercially available or were obtained by precipitation from equimolar aqueous solutions of 0.025 mol / liter Fe (NH ₄ ) ₂ (SO ₄ ) ₂ × 6H ₂ O and 0.025 mol / liter of NH ₄ H ₂ PO ₄ , and hydrogen peroxide produced as an oxidizing agent. In part, the products were subjected to thermal processes to adjust the desired water of hydration.

Iron (III) orthophosphates in different hydrate stages can also be used directly as cathode materials in electrochemical cells without prior lithiation. The above works of Masquellier et al. and Hong et al. start from commercially available amorphous iron (III) phosphates in various hydrate stages. The data on the nominal water of hydration differed from the values experimentally determined by the authors. In one case, ₄ x 4 H ₂ O, a water of hydration content of 3.6 H ₂ O was determined instead of the nominal Hydratwassergehalts FePO, and in the other case, a water of hydration content of 1.6 H ₂ O was determined instead of FePO ₄ • 2H ₂ O. Prosini et al. determined the hydrate water content of a self-produced iron (III) orthophosphate with 1.5 H ₂ O. It is therefore obvious that the water content of crystals in these products can not be set exactly on the manufacturing process. In addition, this manufacturing process leads to undesirable sulfate contamination from the raw materials. Furthermore, the concentrations of the aqueous solutions of the raw materials used are very low, which requires enormous amounts of water in the process. The resulting products are also very fine, which places high demands on the filtration technology in view of the large amounts of liquid phase and also sulfate anions must be washed out.

In the above mentioned work it was shown that amorphous iron (III) phosphates containing water of hydration initially have better electrochemical performance than anhydrates. Hong et al. report, however, that cathodes containing water of hydration in most cases did not even survive 20 charging and discharging cycles. Anhydrates showed significantly better cyclability. Also Prosini et al. could show better cyclability for anhydrates.

task

The object of the invention was therefore to provide a comparison with the prior art improved and easy and inexpensive accessible iron phosphate, which is by electrochemical or chemical Lithiierung in a cathode material for lithium ion batteries or by thermal treatment at low temperatures and short calcination times in a Lithium iron phosphate can be converted over the prior art improved properties.

Description of the invention

The invention comprises a process for the preparation of an amorphous or amorphized iron (III) phosphate anhydrate or a carbon composite of amorphous or amorphized iron (III) phosphate anhydrate, characterized in that iron (III) orthophosphate of the general formula FePO ₄ × 2 H ₂ O or carbon composite of iron (III) orthophosphate of the general formula FePO ₄ × 2 H ₂ O, wherein at least 80% by weight of the iron (III) orthophosphate according to powder X-ray diffraction analysis with CuKα radiation in the phosphosiderite (Metastrengit II) crystal structure, at a temperature in the range of 140 to 250 ° C to a residual water content of 0 to 1 wt .-%, which comprises both bound water of crystallization and free water, and up to a water of crystallization ≤ 0.2 H. ₂ O dehydrated.

Preferably at least 90% by weight, more preferably at least 95% by weight, most preferably at least 99% by weight of the iron (III) orthophosphate according to powder X-ray diffraction analysis with CuKα radiation in the phosphosiderite (Metastrengite II) are present before the dehydration. Crystal structure before.

The invention further comprises amorphous or amorphized iron (III) phosphate anhydrate or carbon composite of amorphous or amorphized iron (III) phosphate anhydrate, prepared or preparable by the method of the invention described herein.

In one embodiment of the invention, the amorphous or amorphized ferric phosphate anhydrate or the carbon composite of amorphous or amorphized ferric phosphate anhydrate in the powder X-ray diffraction pattern has peaks at 15.9 ± 0.5, 20.0 ± 0 , 5, 20.95 ± 0.5, 22.4 ± 0.5 and 28.85 ± 0.5 degrees two-theta based on CuKα radiation.

By the method according to the invention described hereinbefore disadvantages of the Technology be bypassed. The crystalline iron (III) orthophosphate used in the process or the carbon composite of iron (III) orthophosphate with phosphosiderite (Metastrengit II) crystal structure are already commercially available. By in the DE 10 2007 049 757 , of the DE 10 2009 001 204 as well as the DE 10 2011 003 125 described simple methods, the materials are particularly inexpensive and environmentally friendly to produce.

It has surprisingly been found that the crystalline precursors with phosphosiderite (Metastrengite II) crystal structure used according to the invention can be dewatered by simply heating to temperatures in the range from 140 to 250 ° C. to a residual water content in the range from 0 to 1% by weight. wherein the term residual water content comprises both bound water of crystallization and adsorbed water. Residual water contents of not more than 0.5% by weight are particularly advantageous. In particular, the water of crystallization bound in phosphosiderite, which is a dihydrate, is essentially completely removed. In this simple dehydration, the phosphosiderite completely or almost completely loses its original crystalline character to give an amorphous or amorphized iron (III) phosphate.

The term "amorphized" ferric phosphate anhydrate, in the context of the present invention, refers to a ferric phosphate anhydrate which, in powder X-ray diffraction analysis, no longer shows the sharp peaks characteristic of a predominantly crystalline material, but at best relatively low and low strongly broadened peaks that show the skilled person that the material is predominantly amorphous. An example of such a powder X-ray diffraction pattern of an amorphous iron (III) orthophosphate anhydrate according to the invention is shown in FIG 3 and an amorphous iron (III) orthophosphate anhydrate carbon composite according to the invention 10 Spectrum 2 shown. A completely amorphous material shows no peaks in the powder X-ray diffraction pattern, as can be observed for the product according to the invention after chemical lithiation (see 10 , Diffractogram 3, except for the graphite-evoked reflex).

The crystalline starting material phosphosiderite shows characteristic reflections in the powder X-ray diffraction pattern with peaks at 13.68 ± 0.05, 18.18 ± 0.05, 24.75 ± 0.05, 32.25 ± 0.05, 32.35 ± 0, 05, 34.94 ± 0.05, 35.22 ± 0.05, 42.80 ± 0.05, and 45.16 ± 0.05 degrees two-theta based on CuKα radiation. These reflections characteristic of phosphosiderite can not be identified in the powder diffractogram of the amorphized iron (III) phosphate anhydrate according to the invention. Only a few very weak and extremely broad reflections occur at 15.9 ± 0.5, 20.0 ± 0.5, 20.95 ± 0.5, 22.4 ± 0.5 and 28.85 ± 0, 5 degrees two-theta based on CuKα radiation. Due to the extreme reflex width and low intensity, it is not possible to unambiguously assign a known structure to the only faintly recognizable reflections. One cause of the reflections in the X-ray diffraction pattern still detectable in the amorphized product could be small proportions of strengite remaining in the product according to the invention which were not recognizable in the starting material phosphosiderite in the Puverdiffraktogramm due to their low intensity and low crystalline expression (see 10 Spectra 1 and 2). In the context of the present invention is therefore spoken of an "amorphous iron (III) phosphate anhydrate".

The preservation of the amorphous iron (III) phosphate anhydrate according to the invention from the precursors used was surprising since in the literature ( Reale et al., Chem. Mater. 2003, 15, p. 5051-5058 ) Studies are described, according to which a produced by the authors phosphosiderite at a temperature of 140 ° C in an anhydrous monoclinic allotrope of FePO ₄ , which the authors call FePO ₄ II phase and its crystal structure was clearly assigned. Further, the authors describe that the resulting Fe-OP structural element remained almost unaffected by the original phosphosiderite, although the cell volume decreased by about 27%. This phase remained stable up to a temperature of 550 ° C, from which the formation of an α-quartz analogous FePO ₄ phase began.

The iron (III) orthophosphate used according to the invention with phosphosiderite (Metastrengit II) crystal structure, which according to the methods of DE 10 2007 049 757 , of the DE 10 2009 001 204 as well as the DE 10 2011 003 125 can be produced, thus differs from that of Reale et al. investigated material significantly in terms of its thermal dehydration behavior and phase formation. The morphology of the primary particles of the phosphosiderite used according to the invention (see 6 ) does not change during drainage (see 7 ).

An essential advantage of the amorphous or amorphized iron (III) phosphate anhydrate or its carbon composite according to the invention is that it can be clearly and completely characterized with regard to its stoichiometry via the precursor of the crystalline phosphosiderite. This is not the case with the amorphous FePO ₄ hydrates described in the literature, since compounds which have not been defined at any time can be characterized here. There may be stoichiometric deviation, such. As in the literature described differing water of crystallization, which have a negative effect on the performance of the cathode material after further processing and in the later use as a cathode material, due to the formation of unwanted secondary phases.

A further advantage of the invention is that the inventive amorphous or amorphized iron (III) phosphate anhydrate or its carbon composite and its starting compound can be produced industrially as well as inexpensively and ecologically.

Another advantage of the invention is that the carbon composite of the amorphous or amorphized iron (III) phosphate anhydrate of the present invention retains its electrical conductivity at relatively low carbon levels. Subsequent coating of the amorphized material with carbon is not required.

The amorphized iron (III) phosphate anhydrate or its carbon composite according to the invention can also be obtained without difficulty during the production by selecting a higher drying temperature and can be introduced directly into the process described here for the production of LFP or LFP / C , So far, only carbon composites have been known in crystalline form.

Another advantage of the amorphous or amorphized iron (III) phosphate anhydrate according to the invention is that the material can be lithiated chemically and electrochemically. By contrast, the known crystalline material can only be lithiated thermally, which requires high temperatures and is associated with the known disadvantages, such as undesired crystal growth and sintering of the primary particles.

It was investigated whether the amorphous or amorphized ferric phosphate anhydrate of the present invention can be used directly in half-cells as a cathode material against a lithium anode or using a lithium-containing electrolyte under electrochemical lithiation. Although initially there was no extraordinary activity of the material, the material was readily electrochemically lithiated and delithiated. In this case, the inventive amorphous or amorphized iron (III) phosphate anhydrate showed a rising with increasing number of cycles specific capacity.

The advantages of the amorphous or amorphized iron (III) phosphate anhydrate of the present invention over crystalline material in lithiation are believed to be due to structural differences in the materials. In lithiation, iron (III) is converted to iron (II), and lithium ions are deposited in cavities of the structure to charge balance. The amorphous or amorphized material according to the invention is metastable and presumably already has the required cavities in which the lithium ions can deposit relatively easily. In the crystalline material, these required cavities are initially absent or occupied by water of crystallization. Only at high temperatures, a thermal restructuring takes place, through which the cavities required for the storage of lithium ions are created. This is presumably the reason why the novel amorphous or amorphized iron (III) phosphate anhydrate according to the invention can be lithiated directly electrochemically or chemically, which is not possible with a corresponding crystalline material according to the prior art. The crystalline material can only be lithiated lithically.

If a residual water content is mentioned in the context of the present invention, then this includes both bound water of crystallization and free water or free moisture or residual moisture. In contrast, the crystal water content refers only to the bound water of crystallization. The residual water content is determined according to the invention by determining the loss on ignition of the material by heating to 800 ° C. for 10 minutes. The weight difference before and after this thermal treatment denotes the loss on ignition and thus the residual water content in the sense of this invention.

As described, the novel amorphous or amorphized iron (III) phosphate anhydrate according to the invention can be used directly as cathode material for lithium-ion accumulators. Alternatively, however, the material can also be lithiated chemically and then used directly as a cathode material or, after conversion by calcination into a crystalline material, used as the cathode material.

• a) Eisen(III)orthophosphat der allgemeinen Formel FePO₄ × 2 H₂O oder Kohlenstoff-Komposit von Eisen(III)orthophosphat der allgemeinen Formel FePO₄ × 2 H₂O, wobei wenigstens 80 Gew.-% des Eisen(III)orthophosphats gemäß Pulverröntgenbeugungsanalyse in der Phosphosiderit(Metastrengit II)-Kristallstruktur vorliegen, bei einer Temperatur im Bereich von 140 bis 250°C bis auf einen Restwassergehalt von 0 bis 1 Gew.-%, welcher sowohl gebundenes Kristallwasser als auch freies Wasser umfasst, und bis auf einen Kristallwassergehalt ≤ 0,2 H₂O dehydratisiert,
• b) das dehydratisierte Eisen(III)phosphat oder den dehydratisierten Kohlenstoff-Komposit von Eisen(III)phosphat in Wasser oder wässrigem Lösungsmittel dispergiert und der Dispersion 0,8 bis 1,2 Moläquivalente eines Lithiumsalzes zugibt oder das dehydratisierte Eisen(III)phosphat oder den dehydratisierten Kohlenstoff-Komposit von Eisen(III)phosphat in Wasser oder wässrigem Lösungsmittel dispergiert, welches 0,8 bis 1,2 Moläquivalente eines Lithiumsalzes gelöst enthält, wobei sich Moläquivalente auf die molare Menge an Eisen(III) in der Dispersion und Lithium(I)-Ionen in dem Lithiumsalz beziehen,
• c) die wässrige Dispersion mit 0,9 bis 1,2 Elektronenäquivalenten eines Reduktons umsetzt, wobei ein Elektronenäquivalent Redukton die Menge an Redukton bedeutet, die erforderlich ist, um das in der Dispersion enthaltene Eisen(III) zu Eisen(II) zu reduzieren,
• d) das erhaltene Umsetzungsprodukt bei einer Temperatur im Bereich von 100 bis 300°C und/oder unter vermindertem Druck kleiner als Atmosphärendruck trocknet.

The invention therefore further comprises a process for the preparation of a chemically lithiated iron orthophosphate or iron orthophosphate-carbon composite in which

• a) iron (III) orthophosphate of the general formula FePO ₄ × 2 H ₂ O or carbon composite of iron (III) orthophosphate of the general formula FePO ₄ × 2 H ₂ O, where at least 80% by weight of the iron (III) orthophosphate according to powder X-ray diffraction analysis in the phosphosiderite (Metastrengit II) crystal structure, at a temperature in the range of 140 to 250 ° C to a residual water content of 0 to 1 wt .-%, which comprises both bound water of crystallization and free water, and to dehydrated to a water of crystallization ≤ 0.2 H ₂ O,
• b) the dehydrated iron (III) phosphate or the dehydrated carbon composite of iron (III) phosphate dispersed in water or aqueous solvent and the dispersion 0.8 to 1.2 molar equivalents of a lithium salt or the dehydrated iron (III) phosphate or dispersing the dehydrated carbon composite of iron (III) phosphate in water or aqueous solvent containing 0.8 to 1.2 molar equivalents of a lithium salt, with molar equivalents to the molar amount of iron (III) in the dispersion and lithium ( I) ions in the lithium salt,
• c) reacting the aqueous dispersion with 0.9 to 1.2 electron equivalents of a reductone, one electron equivalent of reductone representing the amount of reductone required to reduce the iron (III) present in the dispersion to iron (II),
• d) drying the resulting reaction product at a temperature in the range of 100 to 300 ° C and / or under reduced pressure less than atmospheric pressure.

Preferably, at least 90% by weight, more preferably at least 95% by weight, most preferably at least 99% by weight of the iron (III) orthophosphate according to powder X-ray diffraction analysis in the phosphosiderite (Metastrengite II) crystal structure are present before dehydration.

From the obtained according to the invention by dehydration amorphous iron (III) phosphate anhydrate can be prepared due to its special properties, a fine aqueous dispersion, with simple stirring of the solid in water as a matrix without addition of excipients is completely sufficient. Of course, it is known to those skilled in the art that various technologies, such as the use of a wet mill, an Ultraturrax, ultrasound and the like and the addition of surfactants, can positively influence the speed and quality of dispersion formation. However, when using surface-active substances, it should be noted that no ionic contaminants are introduced, which later have a negative effect in a battery application. The solids concentration of the dispersion is preferably in the range of 40 to 60 wt .-%.

In step c) of the process according to the invention, iron (III) is reduced to iron (II) using one or more reductones. Reductones are organic compounds which carry two hydroxy groups on the two carbon atoms of a C =C double bond ("endiols") and additionally have a carbonyl group directly on the adjacent carbon atom. The double bond of these endiols is stabilized because of conjugation with the carbonyl group; therefore, the tautomeric equilibrium ("keto-enol tautomerism") is mainly the endiol form and not the keto form. As vinylogous carboxylic acids, reductones are acidic. They have a strong reducing effect.

In this context, one electron equivalent of reductone refers to the amount of reductone required to reduce one mole of iron (III). For example, if one mole of reductone provides two electrons for reduction, such as ascorbic acid, one equivalent of electron equivalent to one mole of iron (III) is equivalent to half a mole of reductone.

When the Fe (III) is reduced to Fe (II), the color of the mixture changes from white-yellowish to black in the case of ferric phosphate anhydrate and from gray to black in the case of the carbon composite of iron ( III) phosphate anhydrate. At the same time, the oxidation of the organic reducing agent takes place instead of intermediates in its oxidative degradation process.

The previously dispersed amorphous iron (III) phosphate anhydrate according to the invention is again divided into smaller units on the basis of primary particles during the reduction, as evidenced inter alia by the fact that the solid fraction obtained can neither be removed nor sedimented by customary filtration methods or by ultracentrifugation.

For this reason, the entire mixture is dried by removing the water at elevated temperature and / or under reduced pressure. A permanent mixing during the drying process is advantageous in order to produce no concentration gradients of any dissolved ingredients of the mixture and to ensure the highest possible homogeneity of the dried mixture.

The 8th and 9 show according to the invention lithiated amorphous Fe (III) PO4 anhydrate-carbon composite after dispersion in water and addition of LiOH, acetic acid and ascorbic acid and after drying at 110 ° C. ( 8th ) and at 200 ° C ( 9 ).

It is interesting that the X-ray diffraction pattern of the lithiated product dried at 110 ° C. shows a completely flat curve ( 10 , Diffractogram 3) in comparison to the amorphized and non-lithiated iron (III) phosphate anhydrate-carbon composite according to the invention, which was dried at 200 ° C. ( 10 , Diffractogram 2). However, if the lithiated product is dried at 200 ° C., a not inconsiderable amount of crystalline LFP / C ( 10 . Spectrum 4). This clearly shows that a reduction of Fe ³⁺ to Fe ²⁺ has taken place in the dispersed solid, wherein the charge compensation takes place by incorporation of previously dissolved Li ⁺ from the dispersion.

The drying of the mixture can optionally be carried out under normal atmosphere and / or under protective atmosphere and / or under reduced pressure. In general, this is a thorough mixing of the mixture, for. As in the tumble dryer, during drying is preferred to counteract segregation processes due to the solubility of some components in the aqueous phase. This ensures a homogeneous distribution of all components present in this mixture. The formation of secondary phases due to concentration gradients with non-homogeneous distribution of the components during optional subsequent calcination can thus be completely suppressed. The X-ray diffraction pattern of a calcined LFP / C produced according to the invention shows exclusively the reflections of LFP and an additional carbon reflex, which does not occur in LFP.

When drying under normal atmosphere, this is preferably a circulating air drying, it comes at higher temperatures from about 100 ° C, preferably 100 to 200 ° C product temperature, the partial surface oxidation of previously reduced by the reductone iron (II). On the other hand, as a result, the proportion of organic constituents introduced by the reductone can be removed, since the oxidative degradation products and intermediates of the reductone are volatile at these temperatures. If this process is carried out under vacuum or at atmospheric pressure reduced pressure, oxidation can be largely prevented, and the organic constituents can also be removed at lower temperatures. This process is preferably used to produce low carbon LFP / C in the range of about 2 to 4 wt%.

The drying under a protective atmosphere, for. B. under nitrogen, or in vacuo at 60 to 350 ° C, the organic components removed only partially. Thus, a carbon content of about 12% by weight was analyzed in a protective atmosphere calcined sample previously dried at 60 ° C under vacuum.

On account of the possible electrochemical lithiation and the direct use of the amorphized iron (III) phosphate anhydrate according to the invention as cathode material and the good performance of LFP or L produced by the amorphous iron (III) phosphate anhydrate according to the invention by calcination, the conclusion is close in that the chemically lithiated amorphous iron (III) phosphate anhydrate can also be used directly as cathode material in electrochemical cells. The advantage of using this variant over the amorphous iron (III) phosphate hydrates used in the literature is that already 1 to 1.05 molar equivalents of lithium cations are present in this compound and thus the lithium required for lithiation is not available via the electrolyte or via the anode - typically metallic lithium foil - must be provided. The advantage over LFP or LFP / C produced by calcination lies in the fact that calcination can be dispensed with.

In one embodiment of the invention, the dried lithiated iron (III) phosphate anhydrate according to the invention or the carbon composite thereof is calcined at a temperature in the range of 400 to 800 ° C for a period of 1 to 24 hours.

Preferably, the calcination of the dried product is carried out at a temperature in the range of 450 to 700 ° C, preferably 500 to 650 ° C and / or for a period of 1 to 12 hours, preferably 2 to 6 hours.

Too high a calcination temperature has the disadvantage that crystal growth and sintering occur to a greater extent. A too low calcining temperature has the disadvantage that non-crystalline areas may remain in the product and / or organic components may possibly remain in the product to a greater extent. Organic constituents can have an electrically insulating effect.

For further reduction of the carbon content in an LFP or LFP / C produced by calcining, an oxygen partial pressure can be set during the calcination. In this case, the oxygen partial pressure can be adjusted so that a partial oxidation of Fe ²⁺ to Fe ²⁺ is compensated by the organic content present in the mixture. The skilled worker is aware that organic additives in the form of z. As hydrocarbons, carbohydrates, polymers or the like or graphite or other carbon modifications ensure efficient reduction of Fe ³⁺ to Fe ²⁺ in a calcination.

Calcination temperatures and residence times can be chosen to induce the formation of a pure LFP phase. The experiments have shown that even at temperatures ≤ 550 ° C pure LFP phases (see 14 ) can be obtained. Furthermore, it has been found that calcining is possible only under a nitrogen atmosphere, ie no forming gas has to be used in order to prevent oxidation and the formation of To prevent secondary phases (see 13 ). The X-ray diffraction pattern clearly shows reflections with high half-widths, which suggests small particles. In comparison, the calcination reflexes at 700 ° C are much sharper (see 15 ).

The resulting LFP or its carbon composite LFP / C may have a specific surface area of> 80 m ² / g. At higher calcination temperatures in the range of 600 to 800 ° C, particle growth occurs due to sintering of the introduced primary particles. Depending on the selected temperature and residence time of the mixture during calcination, a particle size distribution and morphology can be adjusted in a targeted manner. The specific surface of the LFP or LFP / C is also reduced and can be selectively influenced.

Due to the short diffusion distances of a nanoscale material, an LFP sample calcined at not more than 550 ° C has good performance at fast discharge rates. More than 50% of the energy that can be stored under C / 10 can be taken out at a discharge rate of 20C (discharge within 3 minutes). A charging current of 1 C means that a cell whose capacity z. B. with 2 Ah, is charged with a charging current of 2 A for 1 hour and then contains the amount of energy 2 Ah. Charging with C / 10 means that the cell has been charged with one-tenth of the charge current corresponding to its capacity, which, however, takes 10 times as long, ie. H. 10 hours. This convention is commonly used to compare cells without taking into account real capacities. Charging with C / 10 is common in stress tests, as this causes a particularly gentle and complete charge. A discharge rate of 20C means that the discharge is for 1 / 20th-hour, ie. H. in 3 minutes. LFP or LFP / C with low specific surface areas, d. H. larger particles could not be addressed electrochemically at such high discharge rates. All active materials produced show good cycling over 30 load / unload operations at 0.5C / 0.5C.

In a further preferred embodiment of the method according to the invention, the pH of the aqueous dispersion of the dehydrated iron (III) phosphate or the dehydrated carbon composite of iron (III) phosphate before the addition of the lithium salt and before the addition of the reductone to a value ≤ 7.0, preferably ≤ 6.5, more preferably ≤ 6.0 set and / or buffered, wherein for adjusting and / or buffering the pH preferably organic carboxylic acids and / or their anhydrides and / or their lithium salts, particularly preferably formic acid , Acetic acid, propionic acid, n-butanoic acid, pentanoic acid and / or their anhydrides and / or their lithium salts.

If the pH of the aqueous dispersion is too high, this can lead locally to pH values> 7 during the addition of the lithium salt, in particular in the case of LiOH. H. the local buffering effect at the dropping point of the LiOH is insufficient, whereby iron hydroxides or iron oxide hydroxides and / or iron oxide hydrates may form which subsequently do not react as desired.

In a further preferred embodiment of the process according to the invention, the lithium salt is used in an amount of 0.9 to 1.1, more preferably in an amount of 1.0 to 1.05 molar equivalents in the aqueous dispersion and / or the reductone in an amount from 1.0 to 1.05 electron equivalents of the aqueous dispersion used.

If the lithium salt is used in too high an amount, unwanted lithium-rich secondary phases may possibly form in a later calcination reaction. If the lithium salt is used in too low an amount, unwanted lithium-poor secondary phases may possibly form in a later calcination reaction.

If the reductone is used in excess, there is a risk that an excess of reductone will adversely affect the further course of the reactions. Moreover, this is an unnecessary cost aspect. If the reductone is used in an excessively low amount, there is a risk that the reduction of the Fe ³⁺ does not proceed completely and thus no stoichiometric amount of lithium ions is stored.

In a further preferred embodiment of the process according to the invention, the lithium salt in the aqueous dispersion is selected from the group consisting of lithium hydroxide (LiOH), lithium carbonate (Li ₂ CO ₃ ), lithium acetate, lithium formate and mixtures thereof.

The use of these lithium salts has the advantage that the lithium salt does not introduce interfering anion contaminants into the final product, for example sulfate ions or nitrate ions. Organic anions, such as acetate, are oxidized and / or expelled during later calcining.

In a further preferred embodiment of the process according to the invention, the reductone is selected from the group consisting of tartronaldehyde (hydroxypropanedial), ascorbic acid, reductic acid (2,3-dihydroxy-2-cyclopentenone), acetylformoin and mixtures of aforementioned, wherein the reductone is preferably ascorbic acid.

The inventive use of the abovementioned reductones for reducing the iron (III) to iron (II) has the advantage over other known reducing agents that they are compatible with water as a reaction matrix and also have high solubilities, in particular in comparison with alcohols.

In a further preferred embodiment of the process according to the invention, the drying of the reaction product in stage d) takes place with mixing. By permanent mixing during the drying process, the formation of concentration gradients of any dissolved substances is prevented and ensures a high homogeneity of the dried product.

In a further preferred embodiment of the process according to the invention, the dehydrated iron (III) phosphate obtained in stage a) or the dehydrated carbon composite of iron (III) phosphate has peaks in the powder X-ray diffraction pattern at 15.9 ± 0.5, 20.0 ± 0 , 5, 20.95 ± 0.5, 22.4 ± 0.5 and 28.85 ± 0.5 degrees two-theta based on CuKα radiation. This amorphized product has the advantages described herein.

Very particularly advantageous according to the invention is the iron (III) orthophosphate or the carbon composite of iron (III) orthophosphate with phosphosiderite (metastrengite II) crystal structure used according to the invention DE102007049757 . DE102009001204 or DE 102011003125 manufactured or manufacturable product. The contents of the DE102007049757 . DE102009001204 and DE 102011003125 are intended to be encompassed by the disclosure of the disclosure of the present specification.

• 1. Herstellung von Eisen(III)orthophosphat der allgemeinen Formel FePO₄ × nH₂O (n ≤ 2,5), durch ein Verfahren, bei dem man Eisen(II)-, Eisen(III)- oder gemischte Eisen(II,III)-Verbindungen, ausgewählt unter Hydroxiden, Oxiden, Oxidhydroxiden, Oxidhydraten, Carbonaten und Hydroxidcarbonaten, mit Phosphorsäure mit einer Konzentration im Bereich von 5% bis 50% umsetzt, nach der Umsetzung gegebenenfalls vorhandenes Eisen(II) durch Zugabe eines Oxidationsmittels in Eisen(III) überführt und festes Eisen(III)orthophosphat aus dem Reaktionsgemisch abtrennt.
• 2. Vorzugsweise wird die Umsetzung der Eisenverbindungen mit Phosphorsäure bei einer Temperatur im Bereich von 50°C bis 180°C, vorzugsweise im Bereich von 60°C bis 150°C, besonders bevorzugt im Bereich von 70°C bis 120°C durchgeführt.
• 3. Weiterhin vorzugsweise wird die Umsetzung der Eisenverbindungen mit Phosphorsäure unter intensivem Durchmischen durchgeführt.
• 4. Weiterhin vorzugsweise wird die Umsetzung der Eisenverbindungen mit Phosphorsäure für einen Zeitraum von 0,5 min bis 120 min, vorzugsweise von 1 min bis 60 min, besonders bevorzugt von 2 min bis 30 min durchgeführt.
• 5. Weiterhin vorzugsweise wird die Umsetzung der Eisenverbindungen mit Phosphorsäure mit einer Konzentration im Bereich von 8% bis 23% durchgeführt.
• 6. Weiterhin vorzugsweise wird die Oxidation von gegebenenfalls vorhandenem Eisen(II) durch Zugabe von Wasserstoffperoxid (H₂O₂) oder durch Zuführung von Luft, reinem Sauerstoff oder Ozon durchgeführt.
• 7. Weiterhin vorzugsweise wird das Eisen(III)orthophosphat nach der Abtrennung aus dem Reaktionsgemisch bei erhöhter Temperatur und/oder unter vermindertem Druck getrocknet.
• 8. Weiterhin vorzugsweise liegen > 80 Gew.-%, vorzugsweise > 90 Gew.-%, besonders bevorzugt > 95 Gew.-% des Eisen(III)orthophosphats in der Metastrengit II-(Phosphosiderit-)Kristallstruktur vor.
• 9. Weiterhin vorzugsweise besitzt das Eisen(III)orthophosphat zumindest in einer Dimension eine mittlere Primärteilchengröße < 1 μm, vorzugsweise < 500 nm, besonders bevorzugt < 100 nm.
• 10. Weiterhin vorzugsweise weist das Eisen(III)orthophosphat eine Schüttdichte > 600 g/l, vorzugsweise > 800 g/l, besonders bevorzugt > 1000 g/l auf.
• 11. Weiterhin vorzugsweise weist das Eisen(III)orthophosphat einen Gehalt an Natrium und Kalium von jeweils < 300 ppm auf.
• 12. Weiterhin vorzugsweise weist das Eisen(III)orthophosphat einen Schwefelgehalt < 300 ppm auf.
• 13. Weiterhin vorzugsweise weist das Eisen(III)orthophosphat einen Nitratgehalt < 100 ppm auf.

The preparation of iron (III) orthophosphate with phosphosiderite (Metastrengit II) crystal structure according to DE102007049757 includes the following measures:

• 1. Preparation of iron (III) orthophosphate of the general formula FePO ₄ × nH ₂ O (n ≦ 2.5), by a process in which iron (II), iron (III) or mixed iron (II, III) compounds, selected from hydroxides, oxides, oxide hydroxides, oxide hydrates, carbonates and hydroxide carbonates, with phosphoric acid having a concentration in the range of 5% to 50%, after the reaction optionally present iron (II) by adding an oxidizing agent in iron ( III) and solid iron (III) orthophosphate separated from the reaction mixture.
• 2. Preferably, the reaction of the iron compounds with phosphoric acid at a temperature in the range of 50 ° C to 180 ° C, preferably in the range of 60 ° C to 150 ° C, more preferably carried out in the range of 70 ° C to 120 ° C.
• 3. Further preferably, the reaction of the iron compounds with phosphoric acid is carried out with thorough mixing.
• 4. It is further preferred to carry out the reaction of the iron compounds with phosphoric acid for a period of from 0.5 minutes to 120 minutes, preferably from 1 minute to 60 minutes, more preferably from 2 minutes to 30 minutes.
• 5. Further preferably, the reaction of the iron compounds with phosphoric acid is carried out at a concentration in the range of 8% to 23%.
• 6. Further preferably, the oxidation of optionally present iron (II) by addition of hydrogen peroxide (H ₂ O ₂ ) or by supplying air, pure oxygen or ozone is performed.
• 7. Further preferably, the iron (III) orthophosphate is dried after separation from the reaction mixture at elevated temperature and / or under reduced pressure.
• 8. Further preferably,> 80 wt .-%, preferably> 90 wt .-%, particularly preferably> 95 wt .-% of iron (III) orthophosphats in the Metastrengit II (phosphosiderite) crystal structure before.
• 9. Further preferably, the iron (III) orthophosphate has an average primary particle size <1 μm, preferably <500 nm, particularly preferably <100 nm, at least in one dimension.
• 10. Further preferably, the iron (III) orthophosphate has a bulk density> 600 g / l, preferably> 800 g / l, more preferably> 1000 g / l.
• 11. Further preferably, the iron (III) orthophosphate has a content of sodium and potassium of <300 ppm.
• 12. Further preferably, the iron (III) orthophosphate has a sulfur content <300 ppm.
• 13. Further preferably, the iron (III) orthophosphate has a nitrate content <100 ppm.

• 1. Herstellung von Eisen(III)orthophosphat der allgemeinen Formel FePO₄ × nH₂O (n ≤ 2,5) durch ein Verfahren, bei dem man a) eine Fe²⁺-Ionen enthaltende wässrige Lösung herstellt, indem man oxidische Eisen(II)-, Eisen(III)- oder gemischte Eisen(II,III)-Verbindungen, ausgewählt unter Hydroxiden, Oxiden, Oxidhydroxiden, Oxidhydraten, Carbonaten und Hydroxidcarbonaten, zusammen mit elementarem Eisen in ein Phosphorsäure enthaltendes wässriges Medium einbringt und Fe²⁺-Ionen in Lösung bringt und Fe³⁺ mit elementarem Fe (in einer Komproportionierungsreaktion) zu Fe²⁺ umsetzt, b) Feststoffe von der phosphorsauren wässrigen Fe^{2 +}-Lösung abtrennt, c) zu der phosphorsauren wässrigen Fe^{2 +}-Lösung ein Oxidationsmittel zugibt, um Eisen(II) in der Lösung zu oxidieren, und Eisen(III)orthophosphat der allgemeinen Formel FePO₄ × nH₂O ausfällt.
• 2. Vorzugsweise gibt man der phosphorsauren wässrigen Lösung Fällungsreagenzien zu, um Feststoffe aus der Lösung auszufällen und von der phosphorsauren wässrigen Fe^{2 +}-Lösung abzutrennen, und/oder scheidet in der phosphorsauren wässrigen Lösung gelöste Metalle elektrolytische aus der Lösung ab.
• 3. Weiterhin vorzugsweise führt man die Umsetzung der oxidischen Eisenverbindungen zusammen mit elementarem Eisen in Phosphorsäure enthaltendem wässrigem Medium (Stufe a) bei einer Temperatur im Bereich von 15°C bis 90°C, vorzugsweise im Bereich von 20°C bis 75°C, besonders bevorzugt im Bereich von 25°C bis 65°C, und/oder unter intensivem Durchmischen durch.
• 4. Weiterhin vorzugsweise führt man die Umsetzung der oxidischen Eisenverbindungen zusammen mit elementarem Eisen in Phosphorsäure enthaltendem wässrigem Medium (Stufe a) für einen Zeitraum von 1 min bis 120 min, vorzugsweise von 5 min bis 60 min, besonders bevorzugt von 20 min bis 40 min durch.
• 5. Weiterhin vorzugsweise beträgt die Konzentration der Phosphorsäure in dem wässrigen Medium 5% bis 85%, vorzugsweise 10% bis 40%, besonders bevorzugt 15% bis 30%, bezogen auf das Gewicht der wässrigen Lösung.
• 6. Weiterhin vorzugsweise ist das Oxidationsmittel, welches zugegeben wird, um Eisen(II) in der Lösung zu oxidieren, eine wässrige Lösung von Wasserstoffperoxid (H₂O₂), bevorzugt mit einer Konzentration von 15 bis 50 Gew.-%, besonders bevorzugt 30 bis 40 Gew.-%.
• 7. Alternativ ist das Oxidationsmittel, welches zugegeben wird, um Eisen(II) in der Lösung zu oxidieren, ein unter Luft, reinem Sauerstoff oder Ozon ausgewähltes gasförmiges Medium, welches in die wässrige Lösung eingeblasen wird.
• 8. Weiterhin vorzugsweise trennt man das Eisen(III)orthophosphat nach dem Ausfällen von der wässrigen Lösung ab und trocknet es vorzugsweise nach dem Abtrennen bei erhöhter Temperatur und/oder unter vermindertem Druck.
• 9. Weiterhin vorzugsweise besitzt das Eisen(III)orthophosphat zumindest in einer Dimension eine mittlere Primärteilchengröße < 1 μm, vorzugsweise < 500 nm, besonders bevorzugt < 300 nm, ganz besonders bevorzugt < 100 nm.
• 10. Weiterhin vorzugsweise weist das Eisen(III)orthophosphat eine Schüttdichte > 400 g/l, vorzugsweise > 700 g/l, besonders bevorzugt > 1000 g/l und/oder eine Stampfdichte > 600 g/l, vorzugsweise > 750 g/l, besonders bevorzugt > 1100 g/l auf.
• 11. Weiterhin vorzugsweise weist das Eisen(III)orthophosphat einen Gehalt an Natrium und Kalium von jeweils < 300 ppm, vorzugsweise < 200 ppm, besonders bevorzugt < 100 ppm auf und/oder einen Schwefelgehalt von < 300 ppm, vorzugsweise < 200 ppm, besonders bevorzugt < 100 ppm und/oder einen Nitratgehalt von < 300 ppm, vorzugsweise < 200 ppm, besonders bevorzugt < 100 ppm und/oder einen Gehalt an Metallen und Übergangsmetallen, ausgenommen Eisen, von jeweils < 300 ppm, vorzugsweise < 200 ppm, besonders bevorzugt < 100 ppm.

The preparation of iron (III) orthophosphate with phosphosiderite (Metastrengit II) crystal structure according to DE102009001204 includes the following measures:

• 1. Preparation of iron (III) orthophosphate of the general formula FePO ₄ × nH ₂ O (n ≦ 2.5) by a process in which a) an aqueous solution containing Fe ²⁺ ions is prepared by oxidizing oxidic iron ( II), iron (III) or mixed iron (II, III) compounds selected from hydroxides, oxides, oxide hydroxides, oxide hydrates, carbonates and hydroxide carbonates, together with elemental iron in a phosphoric acid-containing aqueous medium is introduced and brings Fe ²⁺ ions in solution and Fe ³⁺ with elemental Fe (in a comproportionation) to Fe ²⁺ reacted, b) separating solids from the phosphoric acid aqueous Fe ²⁺ solution, c) the phosphoric acid aqueous Fe ^{2 +} solution adds an oxidizing agent to oxidize iron (II) in the solution, and iron (III) orthophosphate of the general formula FePO ₄ × nH ₂ O precipitates.
• 2. Preferably is the phosphoric acid aqueous solution precipitation reagents to precipitate solids from the solution and separate ⁺ solution from the phosphoric acid aqueous Fe ^2, and / or eliminated in the phosphoric acid aqueous solution dissolved metals electrolytic from the solution.
• 3. Further preferably, the reaction of the oxidic iron compounds is carried out together with elemental iron in aqueous medium containing phosphoric acid (step a) at a temperature in the range of 15 ° C to 90 ° C, preferably in the range of 20 ° C to 75 ° C, more preferably in the range of 25 ° C to 65 ° C, and / or under intense mixing by.
• 4. Further preferably, the reaction of the oxidic iron compounds together with elemental iron in aqueous medium containing phosphoric acid (step a) for a period of 1 min to 120 min, preferably from 5 min to 60 min, more preferably from 20 min to 40 min by.
• 5. Further preferably, the concentration of phosphoric acid in the aqueous medium is 5% to 85%, preferably 10% to 40%, particularly preferably 15% to 30%, based on the weight of the aqueous solution.
• 6. Further preferably, the oxidizing agent which is added to oxidize iron (II) in the solution, an aqueous solution of hydrogen peroxide (H ₂ O ₂ ), preferably at a concentration of 15 to 50 wt .-%, particularly preferred From 30 to 40% by weight.
• 7. Alternatively, the oxidizing agent added to oxidize iron (II) in the solution is a gaseous medium selected from air, pure oxygen or ozone, which is injected into the aqueous solution.
• 8. Furthermore, the iron (III) orthophosphate is preferably separated off after precipitation from the aqueous solution, and it is preferably dried after separation at elevated temperature and / or under reduced pressure.
• 9. Further preferably, the iron (III) orthophosphate has at least in one dimension an average primary particle size <1 .mu.m, preferably <500 nm, more preferably <300 nm, most preferably <100 nm.
• 10. Further preferably, the iron (III) orthophosphate has a bulk density> 400 g / l, preferably> 700 g / l, more preferably> 1000 g / l and / or a tamped density> 600 g / l, preferably> 750 g / l , particularly preferably> 1100 g / l.
• 11. Further preferably, the iron (III) orthophosphate has a content of sodium and potassium of <300 ppm, preferably <200 ppm, more preferably <100 ppm and / or a sulfur content of <300 ppm, preferably <200 ppm, especially preferably <100 ppm and / or a nitrate content of <300 ppm, preferably <200 ppm, more preferably <100 ppm and / or a content of metals and transition metals, except iron, of <300 ppm, preferably <200 ppm, more preferably <100 ppm.

• 1. Herstellung eines Eisen(III)orthophosphat-Kohlenstoff-Komposits, welcher Eisen(III)orthophosphat der allgemeinen Formel FePO₄ × nH₂O (n ≤ 2,5) enthält, bei dem man eine Kohlenstoffquelle in einer phosphorsauren wässrigen Fe²⁺-Ionen enthaltenden Lösung dispergiert und unter Zugabe eines Oxidationsmittels zu der Dispersion Eisen(III)orthophosphat-Kohlenstoff-Komposit (FOP/C) aus der wässrigen Lösung ausfällt und abtrennt.
• 2. Vorzugsweise wird die wässrige Fe²⁺-Ionen enthaltende Lösung hergestellt, indem man oxidische Eisen(II)-, Eisen(III)- oder gemischte Eisen(II,III)-Verbindungen, ausgewählt unter Hydroxiden, Oxiden, Oxidhydroxiden, Oxidhydraten, Carbonaten und Hydroxidcarbonaten, zusammen mit elementarem Eisen in ein Phosphorsäure enthaltendes wässriges Medium einbringt und Fe²⁺-Ionen in Lösung bringt und Fe³⁺ mit elementarem Fe (in einer Komproportionierungsreaktion) zu Fe²⁺ umsetzt und anschließend Feststoffe von der phosphorsauren wässrigen Fe^{2 +}-Lösung abtrennt.
• 3. Weiterhin vorzugsweise umfasst die Kohlenstoffquelle elementaren Kohlenstoff oder besteht ausschließlich aus elementarem Kohlenstoff, wobei der elementare Kohlenstoff vorzugsweise ausgewählt ist unter Graphit, expandiertem Graphit, Rußen, wie Carbon Black oder Kienruß, Kohlenstoffnanoröhrchen (CNT), Fullerenen, Graphen, Glaskohlenstoff (glasartigem Kohlenstoff), Kohlefasern, Aktivkohle oder Gemischen davon.
• 4. Weiterhin vorzugsweise umfasst die Kohlenstoffquelle neben elementarem Kohlenstoff organische Verbindungen, wobei die organischen Verbindungen vorzugsweise ausgewählt sind unter Kohlenwasserstoffen, Alkoholen, Aldehyden, Karbonsäuren, Tensiden, Oligomeren, Polymeren, Kohlenhydraten oder Gemischen davon.
• 5. Weiterhin vorzugsweise enthält die Dispersion der Kohlenstoffquelle in der phosphorsauren wässrigen Fe²⁺-Ionen enthaltenden Lösung die Kohlenstoffquelle in einer Menge von 1 bis 10 Gew.-% Kohlenstoff, vorzugsweise 1,5 bis 5 Gew.-% Kohlenstoff, besonders bevorzugt 1,8 bis 4 Gew.-% Kohlenstoff, bezogen auf das Gewicht von gefälltem FOP.
• 6. Weiterhin vorzugsweise weist die für die Herstellung der Dispersion verwendete phosphorsaure wässrige Fe²⁺-Ionen enthaltenden Lösung die Fe²⁺-Ionen in einer Konzentration von 0,8 bis 2,0 Mol/l, vorzugsweise 1,0 bis 1,7 Mol/l, besonders bevorzugt 1,1 bis 1,3 Mol/l und/oder einen pH-Wert im Bereich von 1,5 bis 2,5, vorzugsweise 1,8 bis 2,3, besonders bevorzugt 2,0 bis 2,1 auf.
• 7. Weiterhin vorzugsweise ist das Oxidationsmittel, welches der Dispersion zugegeben wird, eine wässrige Lösung von Wasserstoffperoxid (H₂O₂), bevorzugt mit einer Konzentration von 15 bis 50 Gew.-%, besonders bevorzugt 30 bis 40 Gew.-%, oder ein unter Luft, reinem Sauerstoff oder Ozon ausgewähltes gasförmiges Medium, welches in die Dispersion eingeblasen wird.
• 8. Weiterhin vorzugsweise wird der Eisen(III)orthophosphat-Kohlenstoff-Komposit nach dem Ausfällen und Abtrennen von der wässrigen Lösung ein- oder mehrfach mit Wasser, wässrigem und/oder organischem Lösungsmittel gewaschen und anschließend bei erhöhter Temperatur und/oder unter vermindertem Druck getrocknet oder als eine wässrige Dispersion mit einem Feststoffgehalt von 1 bis 90 Gew.-% bereitgestellt.
• 9. Weiterhin vorzugsweise besitzt der Eisen(III)orthophosphat-Kohlenstoff-Komposit zumindest in einer Dimension eine mittlere Primärteilchengröße < 1 μm, vorzugsweise < 500 nm, besonders bevorzugt < 300 nm, ganz besonders bevorzugt < 100 nm.
• 10. Weiterhin vorzugsweise weist der Eisen(III)orthophosphat-Kohlenstoff-Komposit eine Schüttdichte > 400 g/l, vorzugsweise > 700 g/l, besonders bevorzugt > 1000 g/l und/oder eine Stampfdichte > 600 g/l, vorzugsweise > 750 g/l, besonders bevorzugt > 1100 g/l auf.

The preparation of carbon composite of iron (III) orthophosphate with phosphosiderite (Metastrengit II) crystal structure according to DE 102011003125 includes the following measures:

• 1. Preparation of a ferric orthophosphate-carbon composite containing iron (III) orthophosphate of the general formula FePO ₄ .nH ₂ O (n ≤ 2.5), wherein a carbon source in a phosphate-aqueous aqueous Fe ²⁺ -Ionen-dispersed solution and precipitated with the addition of an oxidizing agent to the dispersion iron (III) orthophosphate-carbon composite (FOP / C) from the aqueous solution and separated.
• 2. The aqueous solution containing Fe ²⁺ ions is preferably prepared by reacting oxidic iron (II), iron (III) or mixed iron (II, III) compounds selected from hydroxides, oxides, oxide hydroxides, hydrated oxides, Carbonates and hydroxide, together with elemental iron in an aqueous medium containing phosphoric acid and brings Fe ²⁺ ions in solution and Fe ^{3+ reacted} with elemental Fe (in a Komproportionierungsreaktion) to Fe ²⁺ and then solids from the phosphoric aqueous Fe ^{2 +} Solution separates.
• 3. Further preferably, the carbon source comprises elemental carbon or consists solely of elemental carbon, wherein the elemental carbon is preferably selected from graphite, expanded graphite, carbon blacks or carbon blacks, carbon nanotubes (CNTs), fullerenes, graphene, glassy carbon (glassy carbon ), Carbon fibers, activated carbon or mixtures thereof.
• 4. Further preferably, the carbon source in addition to elemental carbon organic compounds, wherein the organic compounds are preferably selected from hydrocarbons, alcohols, aldehydes, carboxylic acids, surfactants, oligomers, polymers, carbohydrates or mixtures thereof.
• 5. Further preferably, the dispersion of the carbon source in the phosphate-containing aqueous solution containing Fe ²⁺ ions the carbon source in an amount of 1 to 10% by weight of carbon, preferably 1.5 to 5% by weight of carbon, more preferably 1.8 to 4% by weight of carbon, based on the weight of precipitated FOP.
• 6. It is further preferable that the solution containing phosphoric acid Fe ²⁺ ions used for the preparation of the dispersion has the Fe ²⁺ ions in a concentration of 0.8 to 2.0 mol / l, preferably 1.0 to 1.7 Mol / l, more preferably 1.1 to 1.3 mol / l and / or a pH in the range of 1.5 to 2.5, preferably 1.8 to 2.3, particularly preferably 2.0 to 2 , 1 on.
• 7. Further preferably, the oxidizing agent which is added to the dispersion, an aqueous solution of hydrogen peroxide (H ₂ O ₂ ), preferably at a concentration of 15 to 50 wt .-%, particularly preferably 30 to 40 wt .-%, or a selected under air, pure oxygen or ozone gaseous medium which is injected into the dispersion.
• 8. Further preferably, the iron (III) orthophosphate carbon composite after precipitation and separation from the aqueous solution one or more times with water, aqueous and / or organic solvent and then dried at elevated temperature and / or under reduced pressure or as an aqueous dispersion having a solid content of 1 to 90% by weight.
• 9. Furthermore, the iron (III) orthophosphate-carbon composite preferably has an average primary particle size <1 μm, preferably <500 nm, particularly preferably <300 nm, very particularly preferably <100 nm, at least in one dimension.
• 10. Further preferably, the iron (III) orthophosphate-carbon composite has a bulk density> 400 g / l, preferably> 700 g / l, more preferably> 1000 g / l and / or a tamped density> 600 g / l, preferably> 750 g / l, more preferably> 1100 g / l.

The present invention further comprises a lithiated iron phosphate or a lithiated iron phosphate-carbon composite prepared as described herein.

Finally, the invention also encompasses the use of the amorphous or amorphized iron (III) phosphate anhydrate or the carbon composite thereof or the lithiated iron phosphate or the carbon composite thereof according to this invention as a cathode material for lithium-ion secondary batteries.

Use of the lithiated iron phosphate according to the invention or lithiated iron phosphate-carbon composite as cathode material for lithium ion accumulators.

Description of the figures

1 : Electron micrograph (33570 magnification) of iron (III) orthophosphate dihydrate (FePO ₄ .2H ₂ O) with phosphosiderite (metastrengite II) crystal structure prepared according to the prior art.

2 : X-ray diffraction pattern of iron (III) orthophosphate dihydrate (FePO ₄ .2H ₂ O) with phosphosiderite (metastrengite II) crystal structure prepared according to the prior art, according to 1 ,

3 : X-ray diffraction pattern of amorphous iron (III) orthophosphate anhydrate (FOP) prepared by heating to 200 ° C of ferric orthophosphate dihydrate (FePO ₄ × 2 H ₂ O) according to 1 ,

4 X-ray diffraction pattern of iron (III) orthophosphate dihydrate (FePO ₄ .2H ₂ O) having a stringency-crystal structure prepared according to the prior art and a peak list according to PDF maps 33-0667 and 26-1080 (below).

5 : X-ray diffraction pattern of iron (III) orthophosphate dihydrate (FePO ₄ .2H ₂ O) according to 4 after heating to 200 ° C.

6 : Electron micrograph (3730X magnification top and 2130X magnification bottom) of agglomerates of iron (III) orthophosphate dihydrate (FePO ₄ .2H ₂ O) carbon composite (FOP / C) prepared according to DE 10 2011 003 125 Phosphosiderite (Metastrengit II) crystal structure with platelet-shaped morphology of the primary particles.

7 : Electron micrograph (1350X magnification above and 6270X magnification below) of amorphous iron (III) orthophosphate anhydrate carbon composite (FOP / C) prepared by heating to 200 ° C of the FOP / C product according to 6 ,

8th : Electron micrograph (25260x magnification) of amorphous lithium iron (III) orthophosphate carbon composite (LFP / C) prepared according to the invention by dispersion of amorphous iron (III) orthophosphate anhydrate Carbon composite (FOP / C) according to 7 in water, addition of LiOH, acetic acid and ascorbic acid and drying at 110 ° C.

9 : Electron micrograph (11380X magnification) of amorphous lithium iron (III) orthophosphate carbon composite (LFP / C) made according to the invention by dispersion of amorphous iron (III) orthophosphate anhydrate carbon composite (FOP / C) according to 7 in water, addition of LiOH, acetic acid and ascorbic acid and drying at 200 ° C.

• Diffraktogramm 1): Eisen(III)orthophosphat-Kohlenstoffkomposit (FOP/C) mit Phosphosiderit-Kristallstruktur wie gefällt, entwässert und bei 100°C getrocknet;
• Diffraktogramm 2) erfindungsgemäß durch Erhitzen des Stoffes gemäß Diffraktogramm 1) auf 200°C hergestellter amorpher Fe(III)PO₄-Anhydrat-Kohlenstoffkomposit;
• Diffraktogramm 3) erfindungsgemäß aus dem Stoff gemäß Diffraktogramm 2) hergestellter amorpher Fe(III)PO₄-Anhydrat-Kohlenstoffkomposit nach Dispersion in Wasser und Zusatz von LiOH, Essigsäure und Ascorbinsäure und nach Trocknung bei 110°C (gemäß 8);
• Diffraktogramm 4) erfindungsgemäß aus dem Stoff gemäß Diffraktogramm 3) hergestellter Fe(III)PO₄-Anhydrat-Kohlenstoffkomposit nach weiterer Trocknung bei 200°C (gemäß 9);
• Diffraktogramm 5) erfindungsgemäß aus dem Stoff gemäß Diffraktogramm 3) hergestellter lithiierter Fe(III)PO₄-Anhydrat-Kohlenstoffkomposit nach Kalzinieren bei 550°C.

10 X-ray diffraction patterns of the materials from the various stages of the lithiated iron (III) orthophosphate-carbon composite preparation process. Show:

• Diffractogram 1): iron (III) orthophosphate-carbon composite (FOP / C) with phosphosiderite crystal structure as precipitated, dewatered and dried at 100 ° C;
• Diffractogram 2) according to the invention by heating the substance according to the diffractogram 1) to 200 ° C. amorphous Fe (III) PO ₄ anhydrate-carbon composite;
• Diffractogram 3) according to the invention from the substance according to diffractogram 2) prepared amorphous Fe (III) PO ₄ anhydrate-Kohlenstoffkomposit after dispersion in water and addition of LiOH, acetic acid and ascorbic acid and after drying at 110 ° C (according to 8th );
• Diffractogram 4) according to the invention from the substance according to diffractogram 3) prepared Fe (III) PO ₄ -hydrate-carbon composite after further drying at 200 ° C (according to 9 );
• Diffractogram 5) according to the invention from the substance according to diffractogram 3) prepared lithiated Fe (III) PO ₄ anhydrate-Kohlenstoffkomposit after calcination at 550 ° C.

11 : Electron micrograph (27080X magnification) of lithium iron (III) orthophosphate (LFP) produced according to the invention, calcined at 550 ° C. under an N 2 atmosphere.

12 : Electron micrograph (magnification 5840X) of lithium iron (III) orthophosphate (LFP) prepared according to the invention, calcined at 700 ° C.

13 : X-ray diffraction pattern (top) of lithium iron (III) orthophosphate (LFP) prepared according to the invention, calcined at 500 ° C. under N 2 / H 2 atmosphere, and peak list according to PDF map 83-2092 (bottom).

14 : X-ray diffraction pattern of lithium iron (III) orthophosphate carbon composite (LFP / C) prepared according to the invention, calcined at 550 ° C. under N 2 atmosphere and peak list according to PDF maps 40-1499 and 12-0212 (below).

15 : X-ray diffraction pattern of lithium iron (III) orthophosphate carbon composite (LFP / C) prepared according to the invention, calcined at 700 ° C. under N 2 atmosphere and peak list according to PDF maps 81-1173 and 08-0415 (below).

16 : X-ray diffraction pattern of lithium iron (III) orthophosphate (LFP) prepared according to the comparative example in ethanol, calcined at 550 ° C. under N 2 / H 2 atmosphere and peak list according to PDF maps 81-1173 and 08-0415 (below).

17 X-ray diffraction pattern of lithium iron (III) orthophosphate anhydrate (LFP) prepared according to the comparative example in ethanol calcined at 550 ° C under N 2 atmosphere and peak list according to PDF maps 40-1499 and 76-1762 (below).

Examples

Example 1 - Preparation of iron (III) orthophosphate (FOP) according to DE 10 2007 049 757

2.4 l of phosphoric acid solution having a density of 1.121 g / l were heated to 92 ° C and then treated with 130 g of Fe ₃ O ₄ (company Farbu Huzhou Huaman Chem. Ind. Co. Ltd.). The reaction mixture was stirred and after 11 minutes a color change to gray was observed, indicating the end of the reaction. At the previously set temperature, 35 ml of 35% H ₂ O ₂ solution were then added dropwise over 6 minutes in order to oxidize iron (II) present in the reaction mixture to iron (III). The content of iron (II) in the reaction mixture was controlled with appropriate test strips from Merck. As soon as no more iron (II) was detectable, the pink-gray discolored mixture was stirred for a further 15 min. The color changed to pink. The product was filtered off and dried at 150 ° C under atmospheric pressure. Wet yield: 370 g Dry yield: 305 g Yield in%: 96.7 Bulk density: 920 g / l

Example 2 - Preparation of iron (III) orthophosphate (FOP) according to DE 10 2007 049 757

1 l of phosphoric acid solution having a density of 1.133 g / l was heated to 95 ° C and then mixed with 92 g of freshly precipitated iron hydroxide (solids content about 63%). After 5 minutes, a color change to gray. At the previously set temperature 22 ml of 35% H ₂ O ₂ solution were added dropwise within 4 min. The reaction mixture was then held at 100 ° C for 19 min until the color turned to pink. The product was filtered off and dried at 150 ° C at ambient pressure. Wet yield: 214 g Dry yield: 124 g Yield in%: about 93 Bulk density: 890 g / l

Example 3 - Preparation of iron (III) orthophosphate (FOP) according to DE 10 2007 049 757

2.7 l of phosphoric acid solution with a density of 1.09 g / l were heated to 90 ° C and then added in portions with 200 g of a filter cake of freshly precipitated iron hydroxide carbonate (solids content about 48%). During the addition, the temperature rose to 96 ° C. After 5 minutes, a color change to red-gray took place. Thereafter, 20 g of 35% H ₂ O ₂ solution were added within 4 min. The content of iron (II) was again checked with corresponding test strips from Merck. The mixture was then stirred for a further 15 min, filtered and dried at 150 ° C under ambient atmosphere. Wet yield: 193 g Dry yield: 128g Yield in%: about 96 Bulk density: 810 g / l

Example 4 - Preparation of iron (III) orthophosphate (FOP) according to DE 10 2009 001 204

A dilute phosphoric acid (18% by weight, density = 1.146 g / ml at 20 ° C.) was initially charged at room temperature (RT, 20 ° C.) and admixed with 20 g of iron oxide (magnetite, Fe ₃ O ₄ ). The batch was homogenized at 10,000 rpm for 10 minutes with a dispersing rod. Subsequently, the resulting suspension was added with stirring 7 g of iron powder.

It set an exothermic reaction. The temperature increased from about 20 ° C to about 40 ° C within 20 min. The suspension changed color from black to green-brown over this period, and the starting material went into solution. Small bubbles in the suspension showed that gas evolution (H ₂ ) occurred. With a bubble counter, the amount of gas produced was quantified. After the dissolution process was completed, the solution was filtered to separate solids from the solution. The solution was then heated to 80 ° C and mixed with about 55 ml of H ₂ O ₂ solution (35 wt .-%) to oxidize in the solution Fe ²⁺ ions to Fe ³⁺ ions. As a decomposition product of H ₂ O ₂ . oxygen was created. A rapid test for Fe ²⁺ ions (test strips from Merck) was used to check whether the oxidation reaction was complete. If appropriate, H ₂ O _{2 was} added. Subsequently, the now pink-colored solution was kept at about 85 ° C and iron (III) orthophosphate precipitated. The failure took about 30 minutes. The final product was light pink and was filtered off with suction through a frit and washed with 400 ml of water. The finer the material, the longer the suction could take. The product was then dried in a drying oven for 3 h at 80 ° C. The yield was at least 90%. The final product was a fine ferric orthophosphate.

Example 5 - Preparation of iron (III) orthophosphate (FOP) according to DE 10 2009 001 204

As Example 4, but a slightly higher concentrated phosphoric acid was presented (25 wt .-%, density = 1.208 g / ml at 20 ° C), and after the oxidation reaction, the iron (III) orthophosphate was precipitated at 100 ° C. The yield was over 90%. The final product was a crude ferric orthophosphate compared to Example 1.

Example 6 - Preparation of iron (III) orthophosphate (FOP) according to DE 10 2009 001 204

20 g of Fe ₃ O ₄ were initially charged in 125 g of H ₂ O and pretreated with an Ultraturrax at 10,000 rpm for 30 min. Subsequently, 125 g of 75% phosphoric acid, a further 125 g of H ₂ O and 7 g of Fe were added at RT. The density of the diluted phosphoric acid in the batch was 1.146 g / ml at 20 ° C. There was a slight gas evolution that persisted throughout the reaction period. Within 7 minutes, the temperature rose to 42 ° C and the color of the suspension changed to brown. After 9 minutes, no further increase in temperature was detected and therefore the reaction mixture is heated in an oil bath (T = 120 ° C). After 70 minutes, there was a green solution which had very little turbidity. Further gas evolution was no longer observed. The turbidity was removed by filtration and the filtrate was treated with 40 ml of H ₂ O ₂ solution (35% by weight) at 80 ° C. There was a change in color over intense red to light pink, the product precipitated as a fine solid with a light pink color. The yield was 99.8% (71.7 g).

Example 7 - Preparation of iron (III) orthophosphate (FOP) according to DE 10 2009 001 204

20 g of Fe ₃ O ₄ , 7 g of Fe, 250 g of H ₂ O and 125 g of 75% phosphoric acid were combined at RT. The density of the diluted phosphoric acid in the batch was 1.146 g / ml at 20 ° C. There was a slight gas evolution that persisted throughout the reaction period. Within 20 minutes, the temperature rose to 38 ° C and the color of the suspension changed to brown. After 30 minutes, no further increase in temperature was detected and therefore the reaction mixture was heated in an oil bath (T = 120 ° C). After 90 minutes, a green solution was present which had very little turbidity. Further gas evolution was no longer observed. The turbidity was removed by filtration and the filtrate was treated with 40 ml of H ₂ O ₂ solution (35% by weight) at 85 ° C. There was a change in color over intense red to light pink, the product precipitated as a fine solid with a light pink color. The yield was 83.5% (60.0 g).

Example 8 - Preparation of iron (III) orthophosphate (FOP) according to DE 10 2009 001 204

20 g of Fe ₃ O ₄ , 7 g of Fe, 250 g of H ₂ O and 204 g of 75% phosphoric acid were combined at RT. The density of the diluted phosphoric acid in the batch was 1.232 g / ml at 20 ° C. There was a slight gas evolution that persisted throughout the reaction period. Within 10 minutes the temperature rose to 53 ° C and the color of the suspension changed to brown. It was immediately cooled to 50 ° C with the help of an ice bath. After a further 40 minutes at 50 ° C, a green solution was present, which had a very low turbidity. Further gas evolution was no longer observed. The turbidity was removed by filtration and the filtrate was treated with 40 ml of H ₂ O ₂ solution (35% by weight) at 85 ° C. There was a change in color over intense red to light pink, the product precipitated as a coarse solid with a light pink color. The yield was 85.8% (61.6 g).

Example 9 - Preparation of iron (III) orthophosphate (FOP) according to DE 10 2009 001 204

10 g of Fe ₂ O ₃ , 3.2 g of Fe, 211 g of H ₂ O and 93 g of 75% phosphoric acid were combined at 50 ° C. The density of the diluted phosphoric acid in the batch was 1.134 g / ml at 20 ° C. There was a slight gas evolution that persisted throughout the reaction period. After 157 min at 50 ° C, a green solution was present, which had a very low turbidity. Further gas evolution was no longer observed. The turbidity was removed by filtration and the filtrate was washed with 20 ml H ₂ O ₂ solution. (35 wt .-%) at 85 ° C added. There was a change in color over intense red to light pink, the product precipitated as a fine solid with a light pink color. The yield was 30.2 g.

Example 10 - Preparation of iron (III) orthophosphate (FOP) according to DE 10 2009 001 204

10 g of Fe ₂ O ₃ , 11 g of Fe, 379 g of H ₂ O and 168 g of 75% phosphoric acid were combined at RT. The density of the diluted phosphoric acid in the batch was 1.134 g / ml at 20 ° C. There was a slight gas evolution that persisted throughout the reaction period. It was heated to 63 ° C and after 120 min a green solution was obtained, which had a very low turbidity. Further gas evolution was no longer observed. The turbidity was removed by filtration and the filtrate was treated with 30 ml of H ₂ O ₂ solution (35% by weight) at 85 ° C. There was a change in color over intense red to light pink, the product precipitated as a fine solid with a light pink color. The yield was 58.0 g.

Example 11: Preparation of an iron (III) orthophosphate-carbon composite (FOP / C) with 7.3% graphite according to DE 10 2011 003 125

In a stirred tank 2540 g (about 2 L) of Fe ^{2 +} solution were presented and pumped by a stirred ball mill (LabStar, Fa. Netzsch), equipped with grinding balls of 0.4-0.6 mm, in recycle mode. Subsequently, 33.1 g of graphite (UF2 from. Graphitwerk Kropfmühl KG) were added in 4 portions within 5 minutes. The particle size distribution and quality of the dispersion was checked every 30 minutes by means of a DLS measurement (Dynamic Light Scattering, Malvern Zetasizer). After 3 hours no change could be detected compared to the 2 previous measurements. The experiment was stopped and the dispersion collected in a beaker.

1100 g of the dispersion were heated to 75 ° C and then with stirring 110 ml of H ₂ O ₂ (35% in water) was added to initiate the precipitation of FOP. After the decaying gas evolution was stirred for a further 15 minutes at 85 ° C. The solids content of the mixture was separated with a Nutsche filter and then resuspended twice in each 1 L deionized water and filtered. After drying in a convection oven at 100 ° C, 182 g of a gray solid were obtained. The XRD analysis of the product showed the characteristic reflections for phosphosiderite and graphite.

Example 12: Preparation of a ferric orthophosphate-carbon composite (FOP / C) with 7.3% expanded graphite

In a stirred tank 3367 g (about 2.6 L) of Fe ^{2 +} solution were submitted and pumped by a stirred ball mill (LabStar, Fa. Netzsch), equipped with grinding balls of 0.4-0.6 mm, in recycle mode. Subsequently, 43.9 g of expanded graphite (SGL Carbon Co.) were added in 4 portions within 5 minutes. After 2 hours, the dispersion was collected in a beaker.

1500 g of the dispersion were heated to 75 ° C and then added with stirring 160 ml of H ₂ O ₂ (35% in water) to initiate the precipitation of FOP. After the fading away adjusting gas evolution was stirred for an additional 15 minutes at 85 ° C. The solids content of the mixture was separated with a Nutsche filter and then resuspended twice in 1.5 L deionized water and filtered. After drying in a circulating air dryer at 100 ° C., 273 g of a gray solid were obtained. The XRD analysis of the product showed the characteristic reflections for phosphosiderite and graphite.

Example 13: Preparation of a ferric orthophosphate-carbon composite (FOP / C) with 4% pretreated graphite

Before suspension in the ball mill, about 30 g of graphite (SGL Carbon Co.) in 500 ml of conc. HNO ₃ heated under reflux for 1 hour and 30 minutes to boiling. The solid was then separated off via a suction filter, each twice resuspended in 1 L deionized water, filtered and dried in a convection oven at 100 ° C overnight. 13.2 g of the graphite thus treated were added to 1850 g (about 2 L) of Fe ^{2 +} solution in 4 portions within 5 minutes, while the solution by a stirred ball mill (LabStar, Fa. Netzsch), equipped with grinding balls of 0.4-0.6 mm, was pumped in the circulation mode. After 2 hours, the dispersion was collected in a beaker.

800 g of the dispersion were heated to 75 ° C and then added with stirring 110 ml of H ₂ O ₂ (35% in water) to initiate the precipitation of FOP. After the decaying gas evolution was stirred for a further 15 minutes at 85 ° C. The solids content of the mixture was separated with a Nutsche filter and then resuspended twice in each 1 L deionized water and filtered. After drying in a circulating air dryer at 100 ° C., 133 g of a gray solid were obtained. The XRD analysis of the product showed the characteristic reflections for phosphosiderite and graphite.

Example 14: Preparation of a ferric orthophosphate-carbon composite (FOP / C) with 2.3% Ketien Black

23 g of Ketjenblack ^® EC-300J (Messrs. Akzo Nobel) were added in portions within 15 minutes to 5600 g (about 4.5 L) of Fe ^{2 +} solution. The solution was pumped through a stirred ball mill (LabStar, Fa. Netzsch), equipped with grinding balls of 0.8-1.0 mm, in recycle mode. After 3 hours, the dispersion was collected in a beaker.

3.8 kg of the dispersion was heated to 75 ° C and then 390 ml of H ₂ O ₂ (35% in water) was added with stirring to initiate the precipitation of FOP. After the decaying gas evolution was stirred for a further 15 minutes at 85 ° C. The solids content of the mixture was separated with a Nutsche filter and then resuspended twice in each 1 L deionized water and filtered. After drying in a circulating air dryer at 100 ° C., 850 g of a light gray solid were obtained. The XRD analysis of the product showed the characteristic reflections for phosphosiderite and graphite.

Example 15: Preparation of an amorphous or amorphized iron (III) phosphate anhydrate

The production of amorphous or amorphized iron (III) phosphate anhydrate or its carbon composites was carried out by simply annealing iron (III) orthophosphate (FOP) or iron (III) orthophosphate-carbon composite (FOP / C) with phosphosiderite structure according to Examples 1 to 14 at 150 ° C to 220 ° C for 8 to 20 hours under normal atmosphere, protective atmosphere or under vacuum.

Example 16 Preparation of Lithiated Iron (III) Phosphate Anhydrate (LFP)

45.46 g LiOH × 1 H ₂ O were dissolved in 300 ml H ₂ O and then 100 ml of 96% acetic acid were added. In this solution, 100 g of ascorbic acid were dissolved and then added 156 g of amorphous iron (III) phosphate anhydrate according to Example 14 was added. The resulting dispersion was stirred for 2 hours at 60 ° C and then dried at 60 ° C in a vacuum oven for 14 hours. Alternatively, the drying can be carried out at 110 ° C or at 210 ° C in a convection oven for 14 hours.

Example 17: Calcination of Lithiated Iron (III) Phosphate Anhydrate (LFP)

A lithiated iron (III) phosphate anhydrate or carbon composite thereof prepared according to Example 16 was heated to 550 ° C in a quartz reaction tube rotary tube furnace under nitrogen atmosphere for 1.5 hours and then maintained at this temperature for 1 hour , The heater was then turned off and the reaction tube allowed to cool to room temperature.

Alternatively, a lithiated iron (III) phosphate anhydrate or carbon composite thereof prepared in Example 16 was heated to 700 ° C in a quartz reaction tube rotary tube furnace under nitrogen atmosphere for 1.5 hours, and then at that temperature for 1 hour held. The heater was then turned off and the reaction tube allowed to cool to room temperature.

Alternatively, a lithiated ferric phosphate anhydrate or carbon composite thereof prepared according to Example 16 was heated to 700 ° C in 2 hours under a flow of 5% by volume of hydrogen in a nitrogen atmosphere, followed by heating for 2 hours Temperature maintained. The heater was then turned off and the reaction tube allowed to cool to room temperature.

Alternatively, a lithiated iron (III) phosphate anhydrate or carbon composite thereof prepared according to Example 16 was heated to 300 ° C over 2 hours under a flow of 5% by volume of hydrogen in a nitrogen atmosphere, followed by heating for 2 hours Maintained temperature, then heated to 600 ° C within 2 hours and then held at this temperature for 1 hour. The heater was then turned off and the reaction tube allowed to cool to room temperature.

Alternatively, a lithiated iron (III) phosphate anhydrate or carbon composite prepared according to Example 16 was heated to 350 ° C under vacuum within 1.5 hours and then held at that temperature for 1 hour. No condensation products could be observed in the intermediate cold trap. Subsequently, the vacuum was exchanged for a flow of 5 vol .-% hydrogen in a nitrogen atmosphere and the material was heated to 700 ° C within 1.5 hours and held at this temperature for 1 additional hour. The heater was then turned off and the reaction tube allowed to cool to room temperature.

Comparative example: Chemical lithiation in ethanol as liquid medium

24.48 g of lithium acetate dihydrate were dissolved in 2000 ml of ethanol. In this solution, 21.13 g of ascorbic acid were further dissolved and then added 30.16 g of amorphous iron (III) phosphate anhydrate. The resulting dispersion was stirred for 3 hours at 50 ° C and the solid was then filtered and washed with ethanol. The drying took place at room temperature over several days. The material was then heated under a) nitrogen atmosphere or b) 5 vol .-% hydrogen in nitrogen atmosphere over 1.5 hours at 550 ° C and held for 2 hours at this temperature. Both samples a) and b) show a significant proportion of an Fe ₂ P ₂ O ₇ phase (see 15 + 16 ).

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102009001204 A1 [0005]
• US 2010/0065787 A1 [0005, 0006]
• US 6855273 B2 [0006]
• DE 102011003125 [0006, 0007, 0025, 0030, 0072, 0072, 0075, 0084]
• DE 102007049757 [0007, 0025, 0030, 0072, 0072, 0073]
• DE 102009001204 [0007, 0025, 0030, 0072, 0072, 0074]
• US 2009/0311597 [0009, 0009]

Cited non-patent literature

• Wang et al. (Solid State Ionics, 2007, 178, 843-847) [0010]
• Wang et al. [0012]
• Wang et al. [0013]
• Wang et al. [0015]
• Masquellier et al., Journal of The Electrochemical Society, 149 (8) A1037-A1044, 2002 [0017]
• Hong et al., J. Mater. Chem., 2002, 12, 1870-1874 [0017]
• Prosini et al., Journal of The Electrochemical Society, 149 (3) A297-A301, 2002 [0017]
• Masquellier et al. [0018]
• Hong et al. [0018]
• Prosini et al. [0018]
• Hong et al. [0019]
• Prosini et al. [0019]
• Reale et al., Chem. Mater. 2003, 15, p. 5051-5058 [0029]
• Reale et al. [0030]

Claims (15)

Process for the preparation of an amorphous or amorphised iron (III) phosphate anhydrate or a carbon composite of amorphous or amorphized iron (III) phosphate anhydrate, characterized in that iron (III) orthophosphate of the general formula FePO ₄ × 2 H ₂ O or carbon composite of iron (III) orthophosphate of the general formula FePO ₄ × 2 H ₂ O, wherein at least 80% by weight of the iron (III) orthophosphate according to powder X-ray diffraction analysis with CuKα radiation in the phosphosiderite (Metastrengit II) crystal structure are present, at a temperature in the range of 140 to 250 ° C to a residual water content of 0 to 1 wt .-%, which comprises both bound water of crystallization and free water, and dehydrated to a water content of crystallization ≤ 0.2 H ₂ O. Amorphous or amorphized iron (III) phosphate anhydrate or carbon composite of amorphous or amorphized ferric phosphate anhydrate, prepared or preparable according to claim 1. An amorphous or amorphized iron (III) phosphate anhydrate or carbon composite of amorphous or amorphized ferric phosphate anhydrate according to claim 2, characterized in that it has peaks in the powder X-ray diffraction pattern at 15.9 ± 0.5, 20.0 ± 0.5, 20.95 ± 0.5, 22.4 ± 0.5 and 28.85 ± 0.5 degrees two-theta based on CuKα radiation. Process for the preparation of a lithiated iron orthophosphate or a lithiated iron orthophosphate-carbon composite, characterized in that a) iron (III) orthophosphate of the general formula FePO ₄ × 2 H ₂ O or carbon composite of iron (III) orthophosphate of the general formula FePO ₄ × 2 H ₂ O, wherein at least 80% by weight of the iron (III) orthophosphate according to powder X-ray diffraction analysis with CuKα radiation in the phosphosiderite (Metastrengit II) crystal structure are present at a temperature in the range of 140 to 250 ° C to a residual water content of 0 to 1 wt .-%, which comprises both bound water of crystallization and free water, and dehydrated to a water content of crystallization ≤ 0.2 H ₂ O, b) the dehydrated iron (III) phosphate or the dehydrated carbon Composite of iron (III) phosphate dispersed in water or aqueous solvent and the dispersion 0.8 to 1.2 molar equivalents of a lithium salt is added or the d hydrated iron (III) phosphate or the dehydrated carbon composite of ferric phosphate dispersed in water or aqueous solvent containing 0.8 to 1.2 molar equivalents of a lithium salt dissolved, wherein molar equivalents to the molar amount of iron (III c) the aqueous dispersion is reacted with from 0.9 to 1.2 electron equivalents of a reductone, wherein one electron equivalent of reductone means the amount of reductone required to produce the reductone in the dispersion contained iron (III) to reduce iron (II), d) the resulting reaction product at a temperature in the range of 100 to 300 ° C and / or under reduced pressure less than atmospheric pressure. A method according to claim 4, characterized in that further calcining the dried product at a temperature in the range of 400 to 800 ° C for a period of 1 to 24 hours. Method according to one of claims 4 or 5, characterized in that the pH of the aqueous dispersion of the dehydrated iron (III) phosphate or the dehydrated carbon composite of iron (III) phosphate before the addition of the lithium salt and before the addition of the Reduktons to a value ≤ 7.0, preferably ≤ 6.5, more preferably ≤ 6.0 sets and / or buffers, wherein for adjusting and / or buffering the pH preferably organic carboxylic acids and / or their anhydrides and / or their Lithium salts, particularly preferably formic acid, acetic acid, propionic acid, n-butanoic acid, pentanoic acid and / or their anhydrides and / or their lithium salts are used. Method according to one of claims 4 to 6, characterized in that the lithium salt is used in an amount of 0.9 to 1.1, particularly preferably in an amount of 1.0 to 1.05 molar equivalents in the aqueous dispersion and / or the reductone is used in an amount of 1.0 to 1.05 electron equivalents of the aqueous dispersion. Method according to one of claims 4 to 7, characterized in that the lithium salt in the aqueous dispersion is selected from the group consisting of lithium hydroxide (LiOH), lithium carbonate (Li ₂ CO ₃ ), lithium acetate, lithium formate and mixtures thereof. Method according to one of claims 4 to 8, characterized in that the reductone is selected from the group consisting of tartronaldehyde (hydroxypropanedial), ascorbic acid, reductic acid (2,3-dihydroxy-2-cyclopentenone), acetylformoin and mixtures of the foregoing, wherein the reductone is preferably ascorbic acid. Method according to one of claims 4 to 9, characterized in that the drying of Reaction product in step d) is carried out with mixing. Method according to one of claims 5 to 10, characterized in that the calcination of the dried product at a temperature in the range of 450 to 700 ° C, preferably 500 to 650 ° C and / or for a period of 1 to 12 hours, preferably 2 up to 6 hours. A process according to any one of claims 4 to 11, characterized in that the dehydrated iron (III) phosphate obtained in step a) or the dehydrated carbon composite of ferric phosphate in the powder X-ray diffraction pattern has peaks at 15.9 ± 0.5, 20 , 0 ± 0.5, 20.95 ± 0.5, 22.4 ± 0.5 and 28.85 ± 0.5 degrees two-theta based on CuKα radiation. Method according to one of the preceding claims, characterized in that the iron (III) orthophosphate used or the carbon composite of iron (III) orthophosphate with phosphosiderite (Metastrengit II) crystal structure according to DE102007049757, DE102009001204 or DE 102011003125 produced or producible product is. Lithiated iron phosphate or lithiated iron phosphate-carbon composite prepared according to any one of claims 4 to 13. Use of the amorphous or amorphized iron (III) phosphate anhydrate or the carbon composite thereof according to claim 2 or 3 or the lithiated iron phosphate or the carbon composite thereof according to claim 14 as a cathode material for lithium ion secondary batteries.

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