Process for producing a transition metal carbonate in a continuous reactor

Abstract

The present invention relates to a process for producing a transition metal carbonate in a continuous reactor. According to other aspects, the present invention relates to a Li-containing and / or Na-containing transition metal mixed oxide, and to the use of an organic additive for producing a transition metal carbonate as a precursor of an Li-containing and / or Na-containing transition metal mixed oxide.

Description

[0001] Process for the production of a transition metal carbonate in a continuously operated reactor

[0002] The present invention relates to a process for producing a transition metal carbonate in a continuously operated reactor. In further aspects, the present invention relates to a Li- and / or Na-containing transition metal mixed oxide obtainable by this process, as well as to the use of an organic additive for producing a transition metal carbonate as a precursor to a Li- and / or Na-containing transition metal mixed oxide.

[0003] Background of the invention

[0004] The present invention relates to the production of cathode materials for battery applications. Among secondary cells and batteries, comparatively high energy densities are achieved, particularly by lithium-ion batteries. For the positive electrode (cathode) of lithium-ion batteries, lithium-containing layered oxides, such as lithium cobalt oxide (LCO), lithium nickel manganese cobalt oxide (LiNi), are typically used as active materials. x -yMn x Co y O2 (NMC), LiNii- x .yCo x Al y O2 (NCA), lithium iron phosphate LiFePCL (LFP), or LiMn2O4 spinels (LMO), or olivine (LMP, M = Ni, Co, Mn ...) are used. The layered oxides LCO, NMC, and NCA, typically used as cathode active materials in commercial lithium-ion cells, achieve specific capacity values ​​between 150 and 180 mAh / g or higher; lithium manganese spinel (LMO) is used with practical values ​​of around 110 mAh / g.

[0005] Lithium (Li)-containing transition metal mixed oxides, such as Li-rich manganese-nickel mixed oxides (referred to in the state of the art and hereinafter as high-energy (HE) NMx (HE-NMx)) and lithium-nickel-manganese-based spinel-type transition metal oxides (LNMO), are being developed as promising electrode materials for use in lithium-ion batteries, but are not yet in commercial use. Compared to the materials used commercially to date, HE-NMx achieve significantly higher specific capacity values ​​of 250–280 mAh / g. However, these peak values ​​are only achieved at low current rates. The materials are therefore particularly suitable for high-energy applications.

[0006] The prior art describes various manufacturing processes for such active materials, such as HE-NMx.

[0007] In sol-gel synthesis, colloidal dispersions, called sols, are produced from soluble reactants. These sols, upon aging, transform into a solid three-dimensional network, the gel. The gel is a chemical precursor to the final product. The products exhibit a small crystallite size while maintaining a large surface area. However, the manufacturing method is very expensive, making its scaling to industrial scale impractical.

[0008] Pure solid-state synthesis variants are also described, which are used in various ways in the production of battery materials. They are particularly important in the industrial production of LiCoCh as a cathode material. In this process, oxides, carbonates, or other crystalline starting compounds are mixed together and then thermally treated. In contrast to the sol-gel process, the particles used are generally microscopic in size, so the diffusion paths for the reaction are comparatively long.

[0009] From a technical perspective, however, this process is time-consuming and therefore costly if defects in the lattice are not to be left behind, which could impair the electrochemical behavior. The samples obtained in this way achieve higher densities than those from the sol-gel process and have a lower specific surface area. Subsequent milling processes are required to adjust the materials to the desired particle size specification, which in turn increases the technical process's cost. Furthermore, the introduction of impurities during the milling process cannot be ruled out.

[0010] Both of the described methods, sol-gel and solid-state synthesis, require the use of highly pure starting materials. The high quality and purity requirements of the raw materials increase the costs of their provision.

[0011] In addition to these methods, combined processes have been described in which a precursor, e.g., a transition metal carbonate, oxide, or hydroxide, is produced by precipitation, which is then reacted with stoichiometric amounts of a lithium compound to form the final product. Hydroxide coprecipitation is currently widely used in materials for lithium-ion batteries to produce transition metal hydroxide precursors. However, this process is problematic for producing precursors with high manganese content, since Mn 2+ easy to Mn 3+ can be oxidized, producing manganese oxyhydroxide (MnOOH) and leading to a deviation from the desired stoichiometry.

[0012] Carbonate coprecipitation (hereinafter referred to as "carbonate precipitation") therefore emerged as an alternative method for the preparation of transition metal (Mn, Ni, Co) precursors, such as those required for the synthesis of HE-NMx, HE-NMC, or LNMO. In conventional precipitation processes, alkali metal-containing salts, such as sodium carbonate and sodium hydroxide, are used as the carbonate source and base.

[0013] An exemplary process for producing a transition metal carbonate by carbonate precipitation for use as a precursor material for cathode materials in lithium batteries is described in US 2017 / 0309909 A2. The main advantage of carbonate precipitation is that, for all transition metals, the oxidation state of the cations is maintained at 2+ in the carbonate matrix, making the precursors less susceptible to oxidation. The process conditions for carbonate precipitation are also less harsh than those for hydroxide precipitation, as lower pH values ​​can be used. Furthermore, compared to hydroxides, carbonate precipitation leads to more homogeneous products with high capacities. Inert gas is not required during the reaction, which increases the economic efficiency of the process.The purity requirements for the reactants are less stringent in this process, since soluble impurities are washed out during the filtration and washing process of the precipitate and thus do not remain in the product.

[0014] To ensure high functionality of battery active materials, high demands are placed on the purity and particle size of the precursors. Large particles have a slow electrochemical effect due to their kinetics. Particle sizes for battery applications are typically between 1 and 30 pm.

[0015] The state of the art primarily describes batch processes in reactors for the production of manganese nickel carbonates. However, compared to continuously operated reactors, these have the disadvantage that the achievable yield per unit time is significantly lower for a given reactor size. Furthermore, in batch processes, the production capacity per plant is low, as the particles initially precipitate in an undefined manner and can only grow in a defined manner after equilibrium is established. In continuously operated reactors, on the other hand, product can theoretically be withdrawn indefinitely after a single run-in phase. At the same time, productivity can be increased due to the short residence time in the reactor.

[0016] It is known from the literature that during the precipitation of transition metal carbonates in continuously operated reactors, the particle size distribution shifts towards increasingly larger values ​​over time. This creates the problem that during carbonate precipitation in continuously operated reactors, particle sizes of > 30 pm increase over time with longer reaction times, which are unsuitable for battery applications (Wang et al., J. Mater. Chem., 2011, 21, 9290). This means that the reactor must be repeatedly restarted to utilize the usable portion of the product from the synthesis before the particle size increases and makes the product unusable. This disadvantage makes the process uneconomical.

[0017] One way to prevent this growth during carbonate precipitation toward larger particles is to maintain a high pH. However, when alkali metal carbonates are used, this leads to the formation of a mixture of transition metal hydroxides and carbonates. Furthermore, when larger amounts of aqueous ammonia solution are used as a complexing agent, soluble nickel complexes form, which lead to a correspondingly large amount of nickel being removed in this range. In addition, the precursors precipitated in this process contain significant impurities of alkali metal ions. These impurities can lead to inhomogeneous crystallite growth and needle-shaped surface carbonate formation in the final product, which can negatively impact cell capacity (F. Klein et al., ChemSusChem, 2022, 15(20), e202201061; US10411258B2).The aim is to achieve homogeneous crystallite growth and spherical particles with a narrow particle size distribution and small particles, preferably < 30 pm.

[0018] Object of the invention

[0019] The invention is therefore based on the object of producing transition metal precursor materials for Li- and / or Na-containing transition metal oxides in a continuously operated process, which have a particle size suitable for battery applications even during extended operation of the continuously operated reactor. Furthermore, the transition metal precursor materials should be free of impurities that negatively affect cell capacity in battery applications.

[0020] Summary of the invention

[0021] Surprisingly, it was found that the stated object is achieved by using organic additives containing at least one carboxyl and / or hydroxyl group. In particular, it was found that by adding such organic additives to a process for producing a transition metal carbonate in a continuously operated reactor, the particle size of the resulting transition metal carbonate can be specifically adjusted within a range suitable for battery applications.

[0022] The present invention thus provides a process for producing a transition metal carbonate in a continuously operated reactor, comprising:

[0023] (i) mixing an aqueous solution of a transition metal salt with an aqueous solution of a carbonate to precipitate the transition metal carbonate in the reactor and obtain a solid suspension, and

[0024] (ii) continuously removing the solid suspension from the reactor, wherein the precipitation takes place in the presence of an aqueous solution of an organic additive, the organic additive containing one or more carboxyl and / or hydroxyl groups.

[0025] In a further aspect, the present invention provides a Li-containing transition metal mixed oxide, in particular a Li-rich HE-NMx or HE-NMC mixed oxide, obtainable by the process according to the invention.

[0026] In a further aspect, the present invention relates to the use of an organic additive for producing a transition metal carbonate having a particle size D50 in the range of 1 to 30 pm, as a precursor of a Li-containing transition metal mixed oxide, wherein the organic additive contains one or more carboxyl and / or hydroxyl groups.

[0027] Detailed description of the invention

[0028] The technical solution provided by the invention is based on the theoretical concept of reducing the growth rate and nucleation rate of transition metal carbonates during precipitation by adding a suitable additive. The goal is to generate a larger quantity of smaller particles, or rather, to stabilize the crystallization nuclei through steric repulsion at a typically nearly neutral pH value. The reduced electrostatic repulsion of the particles subsequently leads to a reduction in particle size growth and thus to smaller particles in the final product.

[0029] In the prior art, organic additives have already been added to calcium carbonate precipitation to specifically synthesize a specific polymorphic phase (Trushina et al., Materials science & engineering. C, Materials for biological applications, 2014, 45, 644). In contrast, transition metal carbonates, such as those required for the production of precursors for cathode materials, only undergo one modification, so the generation of a polymorphic phase is not to be expected here. Surprisingly, however, it has been shown that the addition of such additives has a strong effect on particle growth in continuous operation during the precipitation of transition metal carbonates. Furthermore, it has been shown that the particle size can be specifically adjusted during the precipitation of transition metal carbonates by selecting and adjusting the amount of the additive added.

[0030] In a first aspect, the present invention thus provides a process for producing a transition metal carbonate in a continuously operated reactor, such as a stirred tank reactor.

[0031] In a first process step, an aqueous solution of a transition metal salt is continuously mixed with an aqueous solution of a carbonate in the presence of an aqueous solution of an organic additive as described herein. This continuous mixing leads to the continuous precipitation of the transition metal carbonate in the reactor. The precipitated transition metal carbonate is thus present as a solid suspension in the reactor and can be continuously removed therefrom.

[0032] After a reactor start-up time, which depends on the reactor type, a chemical equilibrium is reached in the reactor with a constant supply of reactants and continuous removal of the resulting solid suspension. This allows, theoretically, any desired reaction time and product removal time. The reactor type is not particularly limited as long as it is a continuously operated reactor. The precipitation reaction typically takes place in a continuously operated stirred tank reactor (CSTR). Suitable reactors are described, for example, in US Pat. No. 10,833,321 B2 and EP 15 848 741 B1. The reaction can also be carried out in a continuous reactor with Taylor-Couette geometry.Continuous reactors generally have a smaller volume compared to batch reactors and allow for the uninterrupted addition of reagents and reactants and a continuous outflow of the product. For the precipitation of precursors for battery materials, typical residence times of a CSTR range from 30 minutes to 6 hours, although this is not a limitation.

[0033] A residence time (T) is the time in which the reactor contents—measured by volume flow—are exchanged once. A longer residence time generally results in more spherical particles, but also in a lower specific product yield. Residence times between 1 and 4 hours are therefore preferred. Typical reactor operating temperatures are in the range of 20 and 60 °C, preferably in the range of 40 and 60 °C.

[0034] The reactants are typically fed continuously to the reactor as aqueous solutions. Additionally or alternatively, ammonia (NH3) and / or carbon dioxide (CO2) can also be fed to the reactor in gaseous form. In this case, the formation of ammonium carbonate or ammonium bicarbonate occurs in the aqueous solution within the reactor.

[0035] The transition metal salt can be used as a single salt or as a mixture of different transition metal salts. The transition metal of the transition metal salt(s) typically comprises one or more elements selected from Ni, Mn, and Co. Precursors containing Ni and Mn, and optionally Co, are particularly preferred for the production of precursor materials for the production of highly active cathode materials for battery applications.

[0036] Furthermore, in the process according to the invention, the resulting transition metal carbonate can be doped with further metals by adding further metal salts. In this way, not only pure-phase products but also multiphase products doped with different metals can be obtained. For this purpose, one or more further metal salts are added to the reactor. Alternatively, these metal salts can also already be present in the aqueous solution of the transition metal salt. In this embodiment, an aqueous solution comprising a mixture of a transition metal salt with one or more further metal salts is fed to the reactor. Alternatively, the further metals can also already be present in the transition metal salt. The metal salts are usually one or more metal salts, wherein the metal is selected from one or more of the elements Mg, Ca, Zn, Fe and Cu.The anion of the transition metal salt and, optionally, of the one or more further metal salts is not particularly limited, as long as the salt or salts are soluble in water or an aqueous solvent and can thus be fed to the reactor as an aqueous solution. Preferably, the transition metal salt and / or the metal salt(s) are in the form of a sulfate, nitrate, chloride, or acetate, which generally have high aqueous solubility, particularly preferably as sulfate or nitrate, for example nickel sulfate hexahydrate (NiSO46H2O) and manganese sulfate monohydrate (MnSO4H2O).

[0037] A molar ratio of the amounts of transition metal salt (TM) to the one or more further metal salts (M) is typically in the range M / TM=0.2 to 1.0, preferably from 0.5 to 0.9, particularly preferably from 0.7 to 0.8. Furthermore, the molar ratio Mn / TM is typically within the aforementioned ranges.

[0038] To achieve high carbonate precipitation efficiency and economical reactor operation, the concentration of the aqueous solutions used should be within the range of the respective saturation concentration. Typically, the concentrations of the aqueous solutions used are in the range of 20-100%, preferably in the range of 50-100%, and particularly preferably in the range of 80-100% of the respective saturation concentration.

[0039] The cation of the water-soluble carbonate is not particularly limited, as long as the carbonate is soluble in water or an aqueous solvent and can thus be fed to the reactor as an aqueous solution. The cation of the carbonate is particularly preferably the ammonium ion. Accordingly, ammonium carbonate, such as diammonium carbonate and / or ammonium bicarbonate, is preferably used as the carbonate. In an alternative embodiment, the carbonate can also be sodium carbonate.

[0040] A typical, exemplary precipitation reaction can be represented by the following reaction equation:

[0041] MSÜ4 [M(NO3)2] + (NH4)2CO3MC03Q) + (NH4)2SO4[2 NH4NO3]

[0042] M = Ni, Co, Mn, Mg, Ca, Zn, Cu, etc.

[0043] Alternatively, Wang et al. (J. Mater. Chem., 2011, 21, 9290) describe, for example, the preparation of a transition metal carbonate using nickel sulfate hexahydrate (NiSO·6H2O), manganese sulfate monohydrate (MnSO·H2O), sodium carbonate (Na2CO3), and ammonium hydroxide (NH3H2O) as starting materials to prepare a transition metal carbonate of stoichiometry NiO·3MnO·7CO3.

[0044] In an alternative embodiment of the invention, no aqueous solution of a carbonate is fed to the reactor, but instead or additionally, carbon dioxide is fed as a gas or solid, usually as a gas. In this embodiment, the formation of the carbonate only occurs in the reactor.

[0045] Furthermore, ammonia can be added either as an aqueous solution or in gaseous form. In this case, ammonium carbonate is formed from the added carbon dioxide and ammonia in the reactor, leading to the precipitation of the transition metal carbonate.

[0046] Ammonia can be advantageously used in the process according to the invention, both by feeding it into the reactor as an ammonia solution and as a gas, particularly as a complexing agent, to obtain particularly spherical particles. Furthermore, the present invention has shown that a narrower particle size distribution can be obtained by adding ammonia. In addition, ammonia can also be used to adjust the pH in the reactor during the precipitation reaction. Preferred pH values ​​are, for example, in the range from 6.0 to 10.0, preferably in the range from 6.5 to 8.5, and particularly preferably in the range from 7.0 to 8.0.

[0047] In a continuously operated reactor, such as a CSTR, the production of homogeneous and stoichiometric precursors in the precipitation of transition metal carbonates can depend on the pH of the solution. At higher pH values ​​in the range > pH 8.5, the formation of transition metal complexes can increase, leading to undesirably high proportions of soluble transition metal ions that do not participate in the precipitation reaction. This can consequently reduce the economic viability of the process. Significantly higher pH values ​​also lead to the side reaction of hydroxide precipitation. A mixture of hydroxide and carbonate is generally undesirable. In a pH range of 7.5–8.0, complex formation and thus the concentration of transition metal ions in solution are generally minimized.

[0048] The desired pH range for the precipitation reaction in the continuously operated reactor can be predicted by taking into account the chemical equilibria between the products and reactants and can be adjusted by the appropriate addition of the reactants to the reactor.

[0049] The type of organic additive is not particularly limited, as long as the organic additive has suitable aqueous solubility (at standard conditions of 25°C and 1013 hPa) so that it can be fed into the reactor as an aqueous solution. Furthermore, it is desirable that the organic additive is inert and thus does not react chemically with the other reactants and products in the reactor. Furthermore, the organic additive should not form gels.

[0050] Typically, the organic additive is a molecule containing one or more carboxyl and / or one or more hydroxyl groups. Such organic additives are described in the prior art for calcite precipitation, for example in: Trushina et al., Materials science & engineering. C, Materials for biological applications, 2014, 45, 644, and Amjad et al., in Water Soluble Polymers, Solutions Properties and Applications (Ed.: Z. Amjad), Kluwer Academic Publishers, Boston, MA, 2002, 131-147) and can also be advantageously used in the present invention for the precipitation of transition metal carbonates. Amjad et al. describe that additives with a high number of ionizable groups in the molecule exert a stronger inhibitory effect on particle growth than molecules with only a small number of ionizable groups.

[0051] Preferably, the organic additive is selected from lignin, tannin, polyacrylic acid, fulvic acid, salicylic acid, polyvinyl alcohol, amino acids, bovine serum albumin, polyvinylpyrrolidone, benzenehexacarboxylic acid, benzene-1,3,5-tricarboxylic acid, polymaleic acid, copolymers of acrylic acid and / or maleic acid monomers, organophosphonates and mixtures thereof.

[0052] Typically, the organic additive is a polymeric acid, such as one of the acids listed above. The molecular weight of the polymeric acid is only limiting insofar as the organic additive is present as an aqueous solution. The molecular weight of organic additives is typically in the range of Mw < 3000 Daltons.

[0053] The amount of additive in the reactor depends in particular on the type of organic additive and is usually in the range from 50 to 5000 ppm, preferably in the range from 100 to 2000 ppm, whereby, in particular for polymeric additives, amounts in the range from 500 to 10,000 ppm, preferably 1,000 to 5,000, for example 2,000, 3,000 or 4,000 ppm, may also be suitable.

[0054] Tannin is usually used in an amount in the range of 50 to 5000 ppm, preferably 100 to 1000 ppm, particularly preferably 200 to 500 ppm.

[0055] Poly(acrylic acid) (Mw in the range of 500 to 3,000 Da, preferably 1,000 to 2,000 Da) is usually used in an amount in the range of 500 to 50,000 ppm, preferably 1,000 to 10,000 ppm, particularly preferably 2,000 to 5,000 ppm.

[0056] The organic additive can be advantageously used in the process according to the invention to adjust the desired particle size D50 of the precipitated transition metal carbonate as desired, depending on the type and amount of the organic additive used. Nucleation and growth of the particles can be investigated during the precipitation reaction by monitoring particle sizes and particle size distributions over time in the reactor, and the addition of the organic additive can be adjusted accordingly. Depending on the type of reactor and the process conditions used, there is usually an initial lead time during which the reaction conditions in the reactor are adjusted until chemical equilibrium is achieved. During this lead time, significant changes in both the particle size and particle morphology of the precipitated transition metal carbonate can occur.However, after the lead time and establishment of equilibrium in the reactor, the reactor can be operated continuously for practically any length of time and a homogeneous product can be obtained.

[0057] In particular, it was surprisingly observed that when an organic additive as described herein is added, there is no increase in particle size over time, even with long reactor operation times. Rather, the process according to the invention can produce a homogeneous product with a consistently defined particle size and particle size distribution.

[0058] Typically, the particle size D50 of the precipitated transition metal carbonate is in the range of 1 to 30 pm, determined by laser diffraction according to ISO 13320:2020, preferably in the range of 2 to 25 pm, particularly preferably in the range of 5 to 20 pm, for example in the range of 5 < D50 < 12 pm.

[0059] Typically, the particle size D90 of the precipitated transition metal carbonate is in the range of 1 to 50 pm, determined by laser diffraction according to ISO 13320:2020, preferably in the range of 2 to 40 pm, particularly preferably in the range of 5 to 30 pm, for example in the range of 10 < D90 < 20 pm.

[0060] As previously described, impurities of alkali metal ions, such as Na ions, can lead to inhomogeneous crystallite growth and needle-like surface carbonate formation in the final product, which can negatively impact cell capacity. A high impurity content, in particular, tends to reduce the reversible capacity of the cathode due to the presence of the electrochemically inert second phase. It is therefore generally desirable to obtain pure transition metal precursors for cathode production for Li batteries. It is therefore preferred that the process according to the invention be carried out essentially sodium-free. "Essentially sodium-free" is defined here as a sodium content in the precipitated carbonate of <200 ppm, preferably <100 ppm, particularly preferably <20 ppm.

[0061] In alternative embodiments, however, the presence of alkali metal ions, such as Li, Na, or K, can also be advantageously used, particularly if the precipitated carbonate is to be deliberately doped with alkali metal ions. Such applications are described in the prior art, for example, in US 2017 / 0309909 A1.

[0062] In this alternative embodiment, one or more additional metal salts containing one or more alkali metal elements selected from Li, K, and Na are fed to the reactor. This embodiment has the advantage that an alkali metal-containing transition metal carbonate, for example, a lithium-containing transition metal carbonate, can be obtained during the precipitation. The Li, K, and Na-containing metal salts can be fed to the reactor either separately or together with the transition metal salt and / or together with the metal salt and / or together with the carbonate.

[0063] Furthermore, the metal salt described above, containing one or more of the elements Mg, Ca, Zn, Fe and Cu, may additionally contain one or more of the elements Li, K and Na or be doped with these elements.

[0064] The alkali metal elements can be added either as an additional metal salt and / or in the form of a carbonate, or as a metal salt together with the water-soluble carbonate. Thus, in an alternative embodiment, the ammonium carbonate can contain one or more of the elements Li, K, and Na.

[0065] The alkali metal is preferably present in the form of a carbonate salt. Alternatively, however, it can also be present, as described above, as a component of the metal salt or the transition metal salt.

[0066] In the continuously operated reactor according to the invention, the transition metal carbonate obtained as a precipitated solid can be continuously removed from the reactor. This is typically followed by separation of the aqueous solvent from the precipitated solid, for example by filtration, although other methods such as centrifugation are also possible. The resulting product is then typically washed, for example with water or an aqueous solvent, and then optionally dried by methods known in the art.

[0067] The transition metal carbonate obtained by the process according to the invention is characterized by a small particle size and a narrow particle size distribution, as described above. The particle morphology is typically spherical.

[0068] The washed and optionally dried transition metal carbonate can then be reacted with a Li- or Na-containing compound to form a Li- and / or Na-containing mixed oxide. For this purpose, the resulting transition metal carbonate is usually reacted with a Li- and / or Na-containing compound. The reaction preferably takes place to form a Li-rich layered oxide. The reaction is carried out, for example, by mixing the transition metal carbonate with the Li- and / or Na-containing compound and subsequent calcination at a temperature in the range of 600 to 1100 °C, preferably 800 to 950 °C, for 2 to 48 h, preferably for 5 to 12 h. The calcination can be carried out in several stages, for example in two or three calcination stages, each with a different temperature.For example, calcination can initially be carried out at a lower temperature, for example, at 400 to 800°C for 4 to 12 hours, followed by a further calcination step at a higher temperature, for example, at 800 to 1100°C for 6 to 20 hours. Furthermore, the lithiation or sodiation step can be preceded by a thermal treatment of the transition metal carbonate precursor and the associated conversion into a transition metal oxide precursor. This conversion is carried out, for example, at a lower temperature of 300 to 800°C for 1 to 10 hours. The transition metal oxide can then be converted into a Li- and / or Na-containing transition metal mixed oxide, as described for the transition metal carbonate.

[0069] The particle size and particle size distribution obtained by the carbonate precipitation according to the invention are largely retained in the mixed oxide. Any agglomerates formed during calcination can subsequently be sieved out or broken up again by conventional process steps, such as grinding or stirring, so that the particle sizes and particle size distribution obtained by carbonate precipitation can also be restored for the calcined product.

[0070] Typically, the particle size D50 of the resulting mixed oxide is in the range from 1 to 30 pm, determined by laser diffraction according to ISO 13320:2020, preferably in the range from 2 to 25 pm, particularly preferably in the range from 5 to 20 pm, for example in the range from 5 < D50 < 12 pm.

[0071] Typically, the particle size D90 of the resulting mixed oxide is in the range from 1 to 50 pm, determined by laser diffraction according to ISO 13320:2020, preferably in the range from 2 to 40 pm, particularly preferably in the range from 5 to 30 pm, for example in the range from 10 < D90 < 20 pm.

[0072] Lithium and / or sodium-containing carbonates, hydrogen carbonates or hydroxides, such as Li2CO3, LiOH, Na2CO3 or NaOH, can be used as lithium and / or sodium-containing compounds.

[0073] By mixing the transition metal carbonate and the lithium- and / or sodium-containing compound with other metal compounds, for example other metal salts, and subsequently calcining the mixture, the resulting mixed oxide can be specifically doped with other metals, such as Mg, Ca, Zn, Fe, Al, Ti, Mo, W, Ta, Zr, B, Si, Cr and / or Cu.

[0074] The Li- and / or Na-containing transition metal mixed oxide produced by the inventive process described above is preferably a Na-Mn-Ni-containing mixed oxide or a Li-Mn-Ni-containing mixed oxide, particularly preferably a Li-rich mixed oxide, for example a HE-NMx or HE-NMC. Preference is given to oxides with a layered or spinel structure, in particular NMC or Li- and Mn-rich layered oxides. The terms used here, such as Li / Na-Mn-Ni mixed oxide, HE-MNx or HE-MNC, are not to be understood as exhaustive with regard to the elements contained. Rather, the mixed oxides described in connection with the invention can, as described above, also contain further metals, for example in the form of dopants or substituents.

[0075] A further aspect of the present invention is thus a Li- and / or Na-containing transition metal mixed oxide, in particular a Li-containing transition metal mixed oxide, preferably a Li-rich Mn-Ni-containing mixed oxide, in particular a layered oxide, particularly preferably a HE-NMx with a Li- and Mn-rich layered structure, obtainable by the process according to the invention described herein.

[0076] A further aspect of the present invention is the use of an organic additive as described herein for producing a transition metal carbonate as a precursor of a Li-containing transition metal mixed oxide as described above, in particular a transition metal carbonate having a particle size D50 in the range of 1 to 30 pm, determined by laser diffraction according to ISO 13320:2020.

[0077] The mixed oxides produced according to the invention have a defined and small particle size. Furthermore, they possess a homogeneous particle morphology and chemically homogeneous stoichiometry. Therefore, they are particularly suitable as precursor materials for the production of Li- or Na-rich cathode materials for high-capacity Li- or Na-ion batteries.

[0078] The invention is illustrated by the following examples.

[0079] Description of the illustrations

[0080] Figure 1: Scanning electron microscopy (SEM) images of transition metal carbonates after precipitation in the presence of different amounts of tannin (Example 1).

[0081] Figure 2: Representation of the particle size distribution of the precipitated transition metal carbonates in the presence of different amounts of tannin (Example 1).

[0082] Figure 3: XRD measurements of the precipitated transition metal carbonates (Example 1).

[0083] Figure 4: Representation of the particle size distribution of the precipitated transition metal carbonates in the presence of tannin (50 ppm) at different Mn / Ni ratios of the metal salt solution (Example 2).

[0084] Figure 5: Representation of the particle size distribution of the precipitated transition metal carbonates in the presence of varying amounts of polyacrylic acid (Example 3). Figure 6: Representation of the particle size distribution of the precipitated transition metal carbonates in the presence of tannin (500 ppm) over time (Example 4).

[0085] Figure 7: Representation of the particle size distribution of the precipitated transition metal carbonates in the presence of tannin (500 ppm) during precipitation with a Ni-rich metal salt solution (Mn / Ni ratio of Mn / Ni < 1) (Example 5).

[0086] Figure 8: Representation of the particle size distribution measured by laser diffraction of the precipitated transition metal carbonates when varying the reaction parameters (Comparative Example 6).

[0087] Figure 9: Scanning electron microscopy (SEM) images of transition metal carbonates after precipitation without additive while varying the reaction parameters (Comparative Example 6).

[0088] Figure 10: Representation of the particle size distribution measured by laser diffraction of the precipitated transition metal carbonate (sample 12) and the product reacted with a lithium source (sample 13) (Example 7).

[0089] Figure 11: SEM images of a transition metal carbonate (sample 12) and the product reacted with a lithium source (sample 13) (Example 7).

[0090] Examples

[0091] Example 1: Precipitation of transition metal (TM) carbonates with tannin (TA) to adjust the particle size distribution

[0092] An aqueous solution of nickel(II) nitrate hexahydrate [Ni(NOs)2 • 6 H2O] and manganese(II) nitrate tetrahydrate [Mn(NOs)2 • 4 H2O] with a molar ratio of Mn / Ni = 0.65 / 0.35 (samples 1-3) and a total metal concentration of 2.5 mol / kg (3.8 mol / L) was prepared. Furthermore, an aqueous NH4HCO3 solution with a concentration of 2.2 mol / kg (2.3 mol / L) was prepared. The concentration was determined by titration to correct for possible losses due to outgassing of CO2 and NH3. An aqueous solution of tannin (TA) was prepared with different weight proportions depending on the experiment.

[0093] An aqueous solution of tannin was placed in a CSTR (continuously stirred tank reactor, Vnominal = 500 mL, Veffective = 350 mL) (cTannin = CTannin(equilibrium), e.g., 50 ppm). The aqueous solutions of the metal nitrates, NH4HCO3, NH4OH, and tannin were continuously added while stirring at 900 rpm. The temperature in the reactor was kept constant at 40°C. The total flow rate was adjusted so that the reactor contents were exchanged within 30 min. The flows of the individual components were kept constant and monitored throughout the entire experiment by gravimetric dosing. Furthermore, the transition metal (TM) concentration (theoretical solids content of 9%) in the reactor, the molar flow ratio (TM / HCCU = 1.5; TM / NH4OH = 1.0), and the weight fraction of tannin in the reactor were kept constant. Samples (approx. 5 mL) were taken at regular intervals and characterized by laser diffraction.

[0094] After reaching reaction equilibrium in the reactor (after approximately 3 h), a sample was collected over one hour, continuously filtered (Whatman Grade 44), washed with Millipore water, and oven dried at 120°C overnight. For XRD (powder X-ray diffraction) analysis, an aliquot was removed before drying and dried in a stream of argon (Ar) at room temperature.

[0095] To keep the influence of the other reaction parameters constant, only the tannin concentration was varied. The resulting differences in pH lead to slightly different Mn / Ni ratios in the precipitated transition metal carbonate product. With increasing tannin concentrations, the influence of the acidic nature of the tannin also increases, leading to a slight decrease in the pH in the reactor.

[0096] The samples were characterized by ICP-OES (trace element analysis by inductively coupled plasma optical emission spectrometry; elements: Mn, Ni, Na), scanning electron microscopy, and XRD. The results are listed in Table 1.

[0097] Table 1:

[0098] The successful, phase-pure precipitation of the transition metal carbonates was demonstrated by XRD studies (Figure 3). The reflections observed in the XRD measurements can be assigned to the rhodochrosite structure (space group R-3c).

[0099] It was further demonstrated that with increasing tannin concentration, the particle size of precipitated transition metal carbonate decreases significantly, and particle sizes (d50) of <30 pm were obtained (Figures 1 and 2). This allows the desired particle size to be adjusted by varying the amount of tannin under constant synthesis conditions. Furthermore, it was demonstrated that the process can be carried out without sodium, thus avoiding the negative effect of Na ions on the final product in the prior art (see US10411258B2). Example 2: Precipitation of Transition Metal (TM) Carbonates with Tannin (TA) - Variation of TM Stoichiometry I

[0100] An aqueous solution of nickel(II) nitrate hexahydrate [Ni·CH·H·H·6·H·O] and manganese(II) nitrate tetrahydrate [Mn(NO·S·H·H·4·H·O] with a molar ratio of Mn / Ni = 0.65 / 0.35 (sample 3) and Mn / Ni = 0.63 / 0.37 (sample 4) and a total metal concentration of 2.5 mol / kg (3.8 mol / L) was prepared. Furthermore, an aqueous NH4HCO3 solution with a concentration of 2.2 mol / kg (2.3 mol / L) was prepared. The concentration was determined by titration to correct for possible losses due to outgassing of CO2 and NH3. An aqueous solution of tannin (Sigma-Aldrich, 0.8-0.9 wt.%) was also prepared.

[0101] An aqueous tannin solution (50 ppm tannin) was placed in a CSTR (V nominal = 500 mL, V effective = 350 mL), and the aqueous solutions of the metal nitrates, NH4HCO3, NH4OH, and tannin were continuously added while stirring at 900 rpm. The temperature in the reactor was kept constant at 40°C. The total flow rate was adjusted so that the reactor contents were exchanged within 30 min. The flows of the individual components were kept constant and monitored throughout the entire experiment by gravimetric dosing. Furthermore, the transition metal concentration (theoretical solids content of 9%) in the reactor, the molar flow ratio (TM / HCCl' = 1.5; TM / NH4OH = 1.0), and the weight fraction of tannin in the reactor were kept constant. Samples (approx. 5 mL) were taken at regular intervals and characterized by laser diffraction.

[0102] After reaching reaction equilibrium in the reactor (after approximately 3 h), a sample was collected over one hour, continuously filtered (Whatman Grade 44), washed with Millipore water and dried in an oven at 120°C overnight.

[0103] To keep the influence of the other reaction parameters constant, only the Ni / Mn ratio in the metal salt solution was varied. A comparison of Sample 3 and Sample 4 shows that a higher nickel content in the starting solution leads to a slight shift in the particle size distribution from large to smaller values ​​(Figure 4). The samples were analyzed by complexometric titration (elements: Mn, Ni). The results are listed in Table 2.

[0104] Table 2: Example 3: Precipitation of transition metal(TM) carbonates with polyacrylic acid to adjust the particle size distribution

[0105] An aqueous solution of nickel(II) nitrate hexahydrate [Ni·CH·H·H·6·H·O] and manganese(II) nitrate tetrahydrate [Mn(NO·S·H·H·O] 2 · 4·H·O] with a molar ratio of Mn / Ni = 0.65 / 0.35 and a total metal concentration of 2.5 mol / kg (3.8 mol / L) was prepared. Furthermore, an aqueous NH·HCO·H solution with a concentration of 2.2 mol / kg (2.3 mol / L) was prepared. The concentration was determined by titration to correct for possible losses due to outgassing of CO·H·H·O and NH·H·O. An aqueous solution of polyacrylic acid (PAA, M w = 1800, Sigma Aldrich) was prepared with different weight proportions depending on the experiment.

[0106] Water was placed in a CSTR (Vnominal = 500 mL, Veffective = 350 mL), and the aqueous solutions of the metal nitrates, NH4HCO3, NH4OH, and PAA were continuously added while stirring at 900 rpm. The temperature in the reactor was kept constant at 40°C. The total flow rate was adjusted so that the reactor contents were exchanged within 30 min (= 1T, Sample 5) or 3 h (= 1T, Sample 6). The flows of the individual components were kept constant and monitored throughout the entire experiment using a gravimetric dosing control. To maintain the reaction conditions, the transition metal concentration (theoretical solids content of 9%) in the reactor, the molar flow ratio (TM / HCCU = 1.5; TM / NH4OH = 1.0), and the weight fraction of PAA in the reactor were kept constant.

[0107] Samples were taken at regular intervals and characterized by laser diffraction. After reaching reaction equilibrium in the reactor (after approximately 6 T), a larger sample was collected, continuously filtered (Whatman Grade 44), washed with Millipore water, and oven dried at 120°C overnight. The samples were analyzed by complexometric titration (elements: Mn, Ni). The results are listed in Table 3.

[0108] Table 3:

[0109] It was shown that with increasing polyacrylic acid concentration, the particle size of precipitated transition metal carbonate decreases significantly, and particle sizes (d50) of <30 pm can be obtained at 5000 ppm polyacrylic acid (Figure 5). Compared to tannin, slightly larger particles were obtained with the same additive amount. This also allows for the desired particle size to be adjusted for this additive under constant synthesis conditions by varying the amount of polyacrylic acid.

[0110] Example 4: Control of particle size in long-term testing and application in a 1-liter reactor

[0111] An aqueous solution of nickel(II) nitrate hexahydrate [Ni(N)·CH·H·H·6·H·O] and manganese(II) nitrate tetrahydrate [Mn(NO·S)·4·H·O] with a molar ratio of Mn / Ni = 0.65 / 0.35 and a total metal concentration of 2.5 mol / kg (3.8 mol / L) was prepared. Furthermore, an aqueous NH4HCO3 solution with a concentration of 2.2 mol / kg (2.3 mol / L) was prepared. The concentration was determined by titration to correct for possible losses due to outgassing of CO2 and NH3. An aqueous solution of tannin (Sigma-Aldrich, 0.8 wt.%) was prepared.

[0112] Water was placed in a CSTR (V = 1000 mL), and the solutions of the metal nitrates, NH4HCO3, NH4OH, and tannin were continuously added while stirring at 900 rpm. The temperature in the reactor was kept constant at 40°C. The total flow rate was adjusted so that the reactor contents were exchanged within 1 h. The flows of the individual components were kept constant and monitored throughout the entire experiment using a gravimetric dosing system. To maintain the reaction conditions, the transition metal concentration (theoretical solids content of 9%) in the reactor, the molar flow ratio (TM / HCOf = 1.5; TM / NH4OH = 0.9), and the weight fraction of tannin (500 ppm) in the reactor were kept constant.

[0113] Samples were taken at regular intervals, and the particle size distribution was determined using laser diffraction. After reaching reaction equilibrium in the reactor (after approximately 6 h), sample collection was initiated. The sample was continuously filtered (Whatman Grade 44), washed with Millipore water, and oven-dried overnight at 120°C. The results are listed in Table 4.

[0114] Table 4:

[0115] It was demonstrated that this process can be used to produce carbonate precursors on a kilogram scale. Furthermore, after establishing reactor equilibrium in the presence of 500 ppm tannin in the reactor, a consistent particle size and particle size distribution were achieved over a period of 68 hours (Fig. 6). Minor deviations in the particle size distribution were attributed to measurement inaccuracies (sample after 24 hours of reactor operation) and were not significant.

[0116] Example 5: Precipitation of transition metal (TM) carbonates with tannin (TA) - Variation of TM stoichiometry II

[0117] An aqueous solution of nickel(II) nitrate hexahydrate [Ni(NOs)2 • 6 H2O] and manganese(II) nitrate tetrahydrate [Mn(NOs)2 • 4 H2O] with a molar ratio of Mn / Ni = 0.35 / 0.65 and a total metal concentration of 2.5 mol / kg (3.8 mol / L) was prepared. Furthermore, an aqueous NH4HCO3 solution with a concentration of 2.2 mol / kg (2.3 mol / L) was prepared. The concentration was determined by titration to correct for possible losses due to outgassing of CO2 and NH3. An aqueous solution of tannin (0.08 wt.%) was prepared.

[0118] Water was placed in a CSTR (V = 1000 mL) flushed with N2, and the solutions of the metal nitrates, NH4HCO3, NH4OH, and tannin were continuously added while stirring (900 rpm). The temperature in the reactor was kept constant at 40°C. The total flow rate was adjusted so that the reactor contents were exchanged within 3 h. The flows of the individual components were kept constant and monitored throughout the entire experiment using a gravimetric dosing system. To maintain the reaction conditions, the transition metal concentration (theoretical solids content of 9%) in the reactor, the molar flow ratio (TM / HCCU = 1.5; TM / NH4OH = 0.9), and the weight fraction of tannin (500 ppm) in the reactor were kept constant.

[0119] Samples were taken at regular intervals and the particle size distribution was determined using laser diffraction. After reaching reaction equilibrium in the reactor (after approximately 18 h), the sample was continuously filtered (Whatman Grade 44), washed with Millipore water, and oven-dried overnight at 120°C.

[0120] It was shown that even in reactions with Ni-rich Ni / Mn ratio, the particle size distribution can be kept constant over time by the invention (Figure 7).

[0121] Comparative example 6: Variation of the reaction parameters without additive

[0122] An aqueous solution of nickel(II) nitrate hexahydrate [Ni(NOs)2 • 6 H2O] and manganese(II) nitrate tetrahydrate [Mn(NOs)2 • 4 H2O] with a molar ratio of Mn / Ni = 0.3 / 0.7 and a total metal concentration of 2.6 mol / kg (3.9 mol / L) was prepared. Furthermore, an aqueous NH4HCO3 solution with a concentration of 2.0 mol / kg (2.1 mol / L) was prepared. The concentration was determined by titration to correct for possible losses due to outgassing of CO2 and NH3.

[0123] Water was placed in a CSTR (Vnominal = 500 mL, Veffective = 350 mL) flushed with N2. The aqueous solutions of the metal nitrates, NH4HCO3, and NH4OH were continuously added while stirring at 900 rpm. The temperature in the reactor was kept constant at 60°C. The total flow rate was adjusted so that the reactor contents were exchanged within 3 h. The flows of the individual components were kept constant and monitored throughout the entire experiment using a gravimetric dosing control. To compare the reaction conditions, the transition metal concentration (theoretical solids content of 9%) in the reactor and the molar flow ratio were kept constant: TM / HCCU = 1.0 - 1.5; TM / NH4OH = 0.5 - 2.0. Samples were taken at regular intervals, and the particle size was determined using laser diffraction.

[0124] After reaching reaction equilibrium in the reactor (after approximately 18 h), a sample was collected over three hours, continuously filtered (Whatman Grade 44), washed with Millipore water, and oven dried at 120°C overnight. The samples were characterized by ICP-OES (elements: Mn, Ni, Na) and SEM. The measurement results are listed in Table 5.

[0125] Table 5:

[0126] Comparative Example 6 shows that, regardless of the reaction parameters, precipitation is not technically feasible in the selected pH range without additives, as particle sizes > 30 pm are consistently obtained (Figures 8 and 9). However, such large particles are unsuitable for conversion into highly active cathode materials in lithium batteries.

[0127] Furthermore, it is evident that with increasing pH and ammonia concentration, increased Ni-hexammine complex formation occurs, leading to a higher loss of nickel. This makes the process generally uneconomical. Example 7: Reaction of the precipitated transition metal carbonate with a Li + -Source

[0128] A Mn-Ni carbonate precursor was prepared as described in Example 4 in a 1-liter reactor containing 500 ppm tannin. A homogeneous suspension of 100 g of the precursor, Millipore H2O (110 mL), and lithium hydroxide monohydrate (LiOH • H2O, 54 g) was dried at 120°C overnight.

[0129] The resulting powder was then homogenized in a mortar and calcined at 400°C (6 h), 800°C (10 h) and 900°C (20 h). After the first and second calcination steps, the intermediate product was homogenized again to ensure the most uniform li +distribution. A Li- / Mn-rich layered oxide with a stoichiometry of Li1.20Mno.59Nio.21O2 was obtained.

[0130] The precipitated precursor and the calcined product were analyzed by laser diffraction to determine the particle size distribution (Figure 10) and SEM (Figure 11).

[0131] The particle size distribution obtained for the precipitated precursor was largely retained even after calcination. The slight shift in the particle size distribution to slightly larger values ​​can be attributed to the formation of agglomerates. These can be broken up or sieved in a subsequent process step to obtain the particle size distribution obtained for the precursor.

[0132] Table 6:

Claims

Patent claims 1. A process for producing a transition metal carbonate in a continuously operated reactor, the process comprising: (i) mixing an aqueous solution of a transition metal salt with an aqueous solution of a carbonate to precipitate the transition metal carbonate in the reactor and obtain a solid suspension, and (ii) continuously removing the solid suspension from the reactor, wherein the precipitation takes place in the presence of an aqueous solution of an organic additive, the organic additive containing one or more carboxyl and / or hydroxyl groups.

2. The process according to claim 1, wherein the transition metal is selected from one or more of the elements Ni, Mn and Co.

3. The process according to claim 1 or 2, wherein the aqueous solution of the transition metal salt further comprises an aqueous solution of one or more further metal salts, wherein the metal is selected from one or more of the elements Mg, Ca, Zn, Fe and Cu.

4. A process according to any one of the preceding claims, wherein the water-soluble carbonate is an ammonium carbonate selected from diammonium carbonate and / or ammonium bicarbonate.

5. A process according to any one of the preceding claims, wherein gaseous carbon dioxide is fed to the reactor to form the water-soluble carbonate.

6. A process according to any one of the preceding claims, wherein the organic additive comprises a polymeric acid.

7. A process according to any one of the preceding claims, wherein the organic additive is selected from lignin, tannin, polyacrylic acid, fulvic acid, salicylic acid, polyvinyl alcohol, amino acids, bovine serum albumin, polyvinylpyrrolidone, polymaleic acid, copolymers of acrylic acid and / or maleic acid monomers, organophosphonates and mixtures thereof.

8. A process according to any one of the preceding claims, wherein the additive is present in an amount in the range of 50 to 5000 ppm.

9. A process according to any one of the preceding claims, wherein the particle size D50 of the precipitated transition metal carbonate is in the range of 1 to 30 pm, determined by laser diffraction according to ISO 13320:2020.

10. A process according to any one of the preceding claims, wherein the pH in the reactor during precipitation is in the range of 6.5 to 8.

5.

11. A method according to any one of the preceding claims, further comprising the steps: (iii) separating the aqueous solvent from the solid suspension to obtain the precipitated solid, (iv) if necessary, washing the solid with water or an aqueous solvent, (v) if necessary, drying the solid, and (vi) reacting the solid with a lithium- and / or sodium-containing compound to form a Li- and / or Na-containing transition metal mixed oxide 12. The process according to claim 11, wherein step (vi) is carried out by calcining at a temperature in the range of 600 to 1100 °C.

13. The method according to claim 11 or 12, wherein the Li- and / or Na-containing mixed oxide is a Na-Mn-Ni-containing mixed oxide or a Li-Mn-Ni-containing mixed oxide.

14. Li- and / or Na-containing transition metal mixed oxide obtainable by the process according to claim 13.

15. Use of an organic additive for producing a transition metal carbonate having a particle size D50 in the range of 1 to 30 pm, determined by laser diffraction according to ISO 13320:2020, as a precursor of a Li- and / or Na-containing transition metal mixed oxide, wherein the organic additive contains one or more carboxyl and / or hydroxyl groups.

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