Patent Application
20210214844
The present invention is related to a process for coating an oxide material, said process comprising the following steps:
(a) providing a particulate material selected from lithiated nickel-cobalt aluminum oxides, lithiated cobalt-manganese oxides and lithiated layered nickel-cobalt-manganese oxides,
(b) treating said cathode active material with a metal alkoxide or metal amide or metal hydride or metal chloride or alkyl metal compound,
(c) treating the material obtained in step (b) with gas containing HF,
and, optionally, repeating the sequence of steps (b) and (c),
wherein steps (b) and (c) are carried out in a mixer that mechanically introduces mixing energy into the particulate material, or by way of a moving bed or fixed bed
wherein steps (b) and (c) are carried out at a pressure that is in the range of from 5 mbar to 1 bar above ambient pressure.
Lithium ion secondary batteries are modern devices for storing energy. Many application fields have been and are contemplated, from small devices such as mobile phones and laptop computers through car batteries and other batteries for e-mobility. Various components of the batteries have a decisive role with respect to the performance of the battery such as the electrolyte, the electrode materials, and the separator. Particular attention has been paid to the cathode materials. Several materials have been suggested, such as lithium iron phosphates, lithium cobalt oxides, and lithium nickel cobalt manganese oxides. Although extensive research has been performed the solutions found so far still leave room for improvement.
One problem of lithium ion batteries lies in undesired reactions on the surface of the cathode active materials. Such reactions may be a decomposition of the electrolyte or the solvent or both. It has thus been tried to protect the surface without hindering the lithium ion exchange during charging and discharging. Examples are attempts to coat the surface of the cathode active materials with, e.g., aluminium oxide or calcium oxide, see, e.g., U.S. Pat. No. 8,993,051.
The efficiency of the process, however, may still be improved. Especially in embodiments wherein the particles have a tendency to agglomerate the efficiency sometimes leaves room for improvement both in respect to reaction time and percentage of covered particles as well as percentage of coverage of particles.
It was therefore an objective of the present invention to provide a process by which particulate materials may be coated without an unduly long reaction time wherein such particulate materials have a tendency to form agglomerates. It was further an objective to provide a reactor for performing such a process.
Accordingly, the process as defined at the outset has been found, hereinafter also referred to as inventive process or as process according to the (present) invention. The inventive process is a process for coating a particulate material.
Coated materials as obtained in the context with the present invention refer to at least 80% of the particles of a batch of particulate material being coated, and to at least 75% of the surface of each particle being coated, for example 75 to 99.99% and preferably 80 to 90%.
The thickness of such coating may be very low, for example 0.1 to 5 nm. In other embodiments, the thickness may be in the range of from 6 to 15 nm. In further embodiments, the thickness of such coating is in the range of from 16 to 50 nm. The thickness in this context refers to an average thickness determined mathematically by calculating the amount of metal alkoxide or alkyl metal compound or metal halide or metal amide per particle surface in m2 and assuming a 100% conversion in steps (b) and (c).
Without wishing to be bound by any theory, it is believed that non-coated parts of particles do not react due to specific chemical properties of the particles, for example density of chemically reactive groups such as, but not limited to hydroxyl groups, oxide moieties with chemical constraint, or to adsorbed water.
In one embodiment of the present invention the particulate material has an average particle diameter (D50) in the range of from 3 to 20 μm, preferably from 5 to 16 μm. The average particle diameter can be determined, e.g., by light scattering or LASER diffraction. The particles are usually composed of agglomerates from primary particles, and the above particle diameter refers to the secondary particle diameter.
In one embodiment of the present invention, the particulate material has a specific surface, hereinafter also “BET surface” in the range of from 0.1 to 1.5 m2/g. The BET surface may be determined by nitrogen adsorption after outgassing of the sample at 200° C. for 30 minutes or more and beyond this accordance with DIN ISO 9277:2010.
The inventive process comprises three steps (a), (b) and (c), in the context of the present invention also referred to as step (a), step (b) and step (c).
Step (a) includes providing a particulate material selected from lithiated nickel-cobalt aluminum oxides, and lithiated cobalt-manganese oxide. Examples of lithiated layered cobalt-manganese oxides are Li1+x(CoMnfM4d)1−xO2. Examples of layered nickel-cobalt-manganese oxides are compounds of the general formula Li1+x(NiaCobMncM4d)1−xO2,with M4 being selected from Mg, Ca, Ba, Al, Ti, Zr, Zn, Mo, Nb, V and Fe, the further variables being defined as follows:
zero≤x≤0.2
0.1≤a≤0.95,
zero≤b≤0.5,
0.1≤c≤0.6,
zero≤d≤0.1, and a+b+c+d=1.
In a preferred embodiment, in compounds according to general formula (I)
Li(1+x)[NiaCobMncM4d](1−x)O2 (I)
M4 is selected from Ca, Mg, Al and Ba,
and the further variables are defined as above.
In Li1+x(CoeMnfM4d)1−xO2, e is in the range of from 0.2 to 0.99, f is in the range of from 0.01 to 0.8, the variables M4 and d and x are as defined above, and e+f+d=1.
Examples of lithiated nickel-cobalt aluminum oxides are compounds of the general formula
Li[NihCoiAlj]O2+r. Typical values for r, h, i and j are:
h is in the range of from 0.8 to 0.95,
i is in the range of from 0.015 to 0.19,
j is in the range of from 0.01 to 0.08, and
r is in the range of from zero to 0.4.
Particularly preferred are Li(1+x)[Ni0.33Co0.33Mn0.33](1−x)O2, Li(1+x)[Ni0.5Co0.2Mn0.3](1−x)O2, Li(1+x)[Ni0.6Co0.2Mn0.2](1−x)O2, Li(1+x)[Ni0.7Co0.2Mn0.1](1−x)O2, and Li(1+x)[Ni0.8Co0.1Mn0.1](1−x)O2, each with x as defined above, and Li[Ni0.88Co0.065Al0.055]O2 and Li[Ni0.91Co0.045Al0.045]O2.
Said particulate material is preferably provided without any additive such as conductive carbon or binder but as free-flowing powder. In a preferred embodiment, said particulate material is a non-coated particulate material, for example without any aluminum oxide coating.
In one embodiment of the present invention particles of particulate material such as lithiated nickel-cobalt aluminum oxide or layered lithium transition metal oxide, respectively, are cohesive. That means that according to the Geldart grouping, the particulate material is difficult to fluidize and therefore qualifies for the Geldart C region. In the course of the present invention, though, mechanical stirring is not required in all embodiments.
Further examples of cohesive products are those with a flowability factor ffc≤7, preferably 1≤ffc≤7 (ffc=σ1/σc; σ1—major principle stress, σc,—unconfined yield strength) according to Jenike or those with a Hausner ratio fH≥1.1, preferably 1.6≥fH≥1.1(fH=ρtap/ρbulk; ρtap—tapped density measured after 1250 strokes in jolting volumeter,ρPbulk—bulk density according to DIN EN ISO 60).
In step (b) of the inventive process, the particulate material provided in step (a) is treated with a metal alkoxide or metal amide or alkyl metal compound. The treatment will be described in more detail below.
Steps (b) and (c) of the inventive process are performed in a vessel or a cascade of at least two vessels, said vessel or cascade—if applicable—also being referred to as reactor in the context of the present invention. Preferably, steps (b) and (c) are performed in the same vessel.
In one embodiment of the inventive process, step (b) is performed at a temperature in the range of from 15 to 1000° C., preferably 15 to 500° C., more preferably 20 to 350° C., and even more preferably 150 to 200° C. It is preferred to select a temperature in step (b) at which metal alkoxide or metal amide or alkyl metal compound, as the case may be, is in the gas phase.
Step (b) is carried out at a pressure above ambient pressure. Thus, step (b) is carried out at a pressure in the range of from 5 mbar to 1 bar above ambient pressure, preferably 10 to 150 mbar above ambient pressure and more preferably 10 to 560 mbar above ambient pressure. At sea level, ambient pressure is 105 Pa, but depending on the altitude of the place where the inventive process is performed, ambient pressure may be lower. In a preferred embodiment, step (b) is carried out at a pressure in the range of from 5 to 350 mbar above ambient pressure.
In a preferred embodiment of the present invention, alkyl metal compound or metal alkoxide or metal amide, respectively, is selected from M1(R1)2, M2(R1)3, M3(R1)4−yHy, M1(OR2)2, M2(OR2)3, M3(OR2)4, M3[N(R2)2]4, and compounds of M1 or M2 or M3 with combinations of counterions, for example M1(R1)X, M2(R1)2X, M2R1X2, M3(R1)3X, M3(R1)2X2, M3R1X3, and methyl alumoxane, wherein
R1 are different or equal and selected from hydride or C1-C8-alkyl, straight-chain or branched,
R2 are different or equal and selected from C1-C4-alkyl, straight-chain or branched,
M1 is selected from Mg and Zn,
M2 is selected from Al and B,
M3 is selected from Si, Sn, Ti, Zr, and Hf, with Sn and Ti being preferred,
X is halide, same or different, selected from chloride, bromide, or iodide, with chloride being preferred, the variable y is selected from zero to 4, especially zero and 1.
Metal alkoxides may be selected from C1-C4-alkoxides of alkali metals, preferably sodium and potassium, alkali earth metals, preferably magnesium and calcium, aluminum, silicon, and transition metals. Preferred transition metals are titanium and zirconium. Examples of alkoxides are methanolates, hereinafter also referred to as methoxides, ethanolates, hereinafter also referred to as ethoxides, propanolates, hereinafter also referred to as propoxides, and butanolates, hereinafter also referred to as butoxides. Specific examples of propoxides are n-propoxides and iso-propoxides. Specific examples of butoxides are n-butoxides, iso-butoxides, sec.-butoxides and tert.-butoxides. Combinations of alkoxides are feasible as well.
Examples of alkali metal alkoxides are NaOCH3, NaOC2H5, NaO-iso-CcH7, KOCH3, KO-iso-C3H7, and K—O—C(CH3)3.
Preferred examples of metal C1-C4-alkoxides are Si(OCH3)4, Si(OC2H5)4, Si(O-n-C3H7)4, Si(O-iso-C3H7)4, Si(O-n-C4H9)4, Ti[OCH(CH3)2]4, Ti(OC4H9)4, Zn(OC3H7)2, Zr(OC4H9)4, Zr(OC2H5)4, Al(OCH3)3, Al(OC2H5)3, Al(O-n-C3H7)3, Al(O-iso-C3H7)3, Al(O-sec.-C4H9)3, and Al(OC2H5)(O-sec.-C4H9)2.
Examples of metal alkyl compounds of an alkali metal selected from lithium, sodium and potassium, with alkyl lithium compounds such as methyl lithium, n-butyl lithium and n-hexyl lithium being particularly preferred. Examples of alkyl compounds of alkali earth metals are di-n-butyl magnesium and n-butyl-n-octyl magnesium (“BOMAG”). Examples of alkyl zinc compounds are dimethyl zinc and zinc diethyl.
Examples of aluminum alkyl compounds are trimethyl aluminum, triethyl aluminum, triisobutyl aluminum, and methyl alumoxane.
Examples of metal hydrides are M3H4. A preferred example of metal hydrides is Si2H6. Examples of suitable metal chlorides are M32Cl6 and M2Cl3 and M3Cl4, for example Si2Cl6, TiCl4, Til4, SiCl4 and AlCl3.
Metal amides are sometimes also referred to as metal imides. Examples of metal amides are Na[N(CH3)2], Li[N(CH3)2], Si[N(CH3)2]4 and Ti[N(CH3)2]4.
Examples of compounds of M1 or M2 or M3 with combinations of counterions are AlCl(CH3)2, AlCl2CH3, (CH3)3SiCl, SiO2, CH3SiCl3, and HwSi[N(CH3)2]4−w with w being a number from 1 to 4.
Particularly preferred compounds are selected from metal C1-C4-alkoxides and metal C1-C4-alkyl compounds, and even more preferred is trimethyl aluminum.
In one embodiment of the present invention, the amount of metal alkoxide or metal amide or alkyl metal compound is in the range of 0.1 to 1 g/kg particulate material.
Preferably, the amount of metal alkoxide or metal amide or alkyl metal or metal hydride or metal chloride, compound, respectively, is calculated to amount to 80 to 200% of a monomolecular layer on the particulate material per cycle.
In a preferred embodiment of the present invention, the duration of step (b) is in the range of from 1 second to 2 hours, preferably 1 second up to 10 minutes.
In a third step, in the context of the present invention also referred to as step (c), the material obtained in step (b) is treated with gas containing HF.
In one embodiment of the present invention, step (c) is carried out at a temperature in the range of from 50 to 250° C.
HF may be introduced into step (c) directly or by heating a material that releases HF upon heating, for example ammonium salts of HF, for example NH4F or NH4F·HF or HF·pyridine.
In one embodiment of the present invention, in step (b) cathode active material is treated with a metal alkoxide or metal amide or alkyl metal compound at a pressure that is in the range of from 5 mbar to 1 bar above ambient pressure, and in step (c), the material obtained from step (b) is deactivated with a gas containing HF.
Step (c) is carried out at a pressure above ambient pressure. Thus, step (c) is carried out at a pressure in the range of from 5 mbar to 1 bar above ambient pressure, preferably 10 to 50 mbar above ambient pressure. In the context of the present invention, ambient pressure is as defined in context with step (b).
Steps (b) and (c) may be carried out at the same pressure or at different pressures, preferred is at the same pressure.
Said gas containing fluoride may be introduced, e.g., by treating the material obtained in accordance with step (b) with inert gas saturated with HF, for example with nitrogen saturated with HF or a noble gas saturated HF, for example argon. Saturation may refer to normal conditions or to the reaction conditions in step (c).
On one embodiment of the present invention, step (c) has a duration in the range of from 10 seconds to 2 hours, preferable 1 second to 10 minutes.
In one embodiment, the sequence of steps (b) and (c) is carried out only once. In a preferred embodiment, the sequence of steps (b) and (c) is repeated, for example once or twice or up to 40 times. It is preferred to carry out the sequence of steps (b) and (c) two to six times.
Although the last step (c) may be replaced by a thermal treatment at a temperature in the arrange of from 150° C. to 600° C., preferable 250° C. to 450° C. it is preferred to carry out said step as indicated above.
In a preferred embodiment of the present invention, step (c) is carried out in an atmosphere that is free from carbon dioxide. In the context of the present invention, “free from carbon dioxide” means that the respective atmosphere has a carbon dioxide content in the range of from 0.01 to 500 ppm by weight or even less, preferred are 0.1 to 50 ppm by weight or even less. The CO2 content may be determined by, e.g., optical methods using infrared light. It is even more preferred to use an atmosphere with a carbon dioxide below detection limit for example with infrared-light based optical methods.
Steps (b) and (c) of the inventive process may be carried out continuously or batch-wise.
In one embodiment of the present invention, the reactor in which the inventive process is carried out is flushed or purged with an inert gas between steps (b) and (c), for example with dry nitrogen or with dry argon. Suitable flushing—or purging—times are 1 second to 30 minutes, preferably 1 minute to 10 minutes. It is preferred that the amount of inert gas is sufficient to exchange the contents of the reactor of from one to 15 times. By such flushing or purging, the production of by-products such as separate particles of reaction product of metal alkoxide or metal amide or alkyl metal compound, respectively, with water can be avoided. In the case of the couple trimethyl aluminum and water, such by-products are methane and alumina or trimethyl aluminum that is not deposited on the particulate material, the latter being an undesired by-product.
Various embodiments of reactor design are possible to perform the steps (b) and (c) of the inventive process. Steps (b) and (c) are carried out in a mixer that mechanically introduces mixing energy into the particulate material, for example compulsory mixers and free-fall mixers. While free fall mixers utilize the gravitational forces for moving the particles compulsory mixers work with moving, in particular rotating mixing elements that are installed in the mixing room. In the context of the present invention, the mixing room is the reactor interior. Examples of compulsory mixers are ploughshare mixers, in German also called Lödige mixers, paddle mixers and shovel mixers. Preferred are ploughshare mixers. Ploughshare mixers may be installed vertically or horizontally, the term horizontal or vertical, respectively, referring to the axis around which the mixing element rotates. Horizontal installation is preferred. Preferably, the inventive process is carried out in a ploughshare mixer in accordance with the hurling and whirling principle.
In another embodiment of the present invention, the inventive process may be carried out in a free fall mixer. Free fall mixers are using the gravitational force to achieve mixing. In a preferred embodiment, steps (b) and (c) of the inventive process are carried out in a drum or pipe-shaped vessel that rotates around its horizontal axis. In a more preferred embodiment, steps (b) and (c) of the inventive process are carried out in a rotating vessel that has baffles.
In one embodiment of the present invention a vessel or at least parts of it rotates with a speed in the range of from 5 to 500 revolutions per minute (“rpm”), preferred are 5 to 60 rpm. In embodiments wherein a free-fall mixer is applied, from 5 to 25 rpm are more preferred and 5 to 10 rpm are even more preferred. In embodiments wherein a plough-share mixer is applied, 50 to 400 rpm are preferred and 100 to 250 rpm are even more preferred.
In another embodiment of the present invention, steps (b) and (c) are carried out by way of a moving bed or fixed bed. In a fixed bed process, the particulate material provided in step (a) is placed upon a porous area, for example a sieve plate. Hereby, particulate material provided in step (a) forms a bed. In step (b) a medium, especially an inert gas containing a metal alkoxide or metal amide or alkyl metal compound flows from top to bottom through the bed, and in step (c), gas containing HF, e.g., in the form of HF/nitrogen or HF/air, from bottom to top or from top to bottom through the bed.
In a moving bed process, particulate material provided in step (a) are introduced at the top of a tubular reactor, thereby automatically forming a particle bed. A gas stream containing a metal alkoxide or metal amide or alkyl metal compound flows bottom-up through said bed with a gas velocity that is not sufficient to keep the particle bed in a steady state. Instead, the particle bed moves counter-currently with the gas stream (step (b). Step (c) is carried out accordingly but with gas containing HF instead of metal alkoxide or metal amide or alkyl metal.
In a preferred version of the present invention, which allows for the pneumatic conveying of said particulate material, a pressure difference up to 4 bar is applied. Coated particles may be blown out of the reactor or removed by suction.
In one embodiment of the present invention, the inlet pressure is higher but close to the desired reactor pressure. Pressure drops of gas inlet and in the moving or fixed bed, if applicable, have to be compensated.
In the course of the inventive process strong shear forces are introduced into the fluidized bed due to the shape of the reactor, the particles in the agglomerates are exchanged frequently, which allows for the accessibility of the full particle surface. By the inventive process, particulate materials may be coated in short time, and in particular cohesive particles may be coated very evenly.
In a preferred embodiment of the present invention the inventive process comprises the step of removing the coated material from reactor in which steps (b) and (c) are carried out, respectively, by pneumatic convection, e.g. 20 to 100 m/s.
In one embodiment of the present invention, the exhaust gasses are treated with water at a pressure above ambient pressure and even more preferably slightly lower than in the reactor in which steps (b) and (c) are performed, for example in the range of from 2 mbar to 1 bar more than ambient pressure, preferably in the range of from 4 mbar to 25 mbar above ambient pressure. The elevated pressure is advantageous to compensate for the pressure loss in the exhaust lines.
The sealings necessary for separating the reactor and the exhaust gas treatment vessel from the environment are advantageously equipped with nitrogen flushing.
In one embodiment of the present invention, the gas inlet and the outlet are at opposite positions of the vessel used for the inventive process.
In one embodiment of the present invention, the coated oxide material obtained after step (c) is subjected to an after-treatment step (d), for example a thermal after-treatment at a temperature in the range of from 100 to 500° C. at a pressure in the range of from 1 mbar to 105 Pa over a period in the range of from 5 minutes to 5 hours.
By the inventive process, particulate materials may be coated in short time, and in particular cohesive particles may be coated very evenly. The inventive process allows for good safety because any combustible or even explosive atmosphere may be easily avoided.
The progress of the inventive process may be controlled by mass spectrometry. The inventive process is illustrated by the following working example.
Ambient pressure: 105 Pa.
sccm: standard cubic centimeter/min
I. Cathode Active Materials
I.1. Preparation of a Precursor for Cathode Active Materials
A stirred tank reactor was filled with deionized water. The precipitation of mixed transition metal hydroxide precursor was started by simultaneous feed of an aqueous transition metal solution and an alkaline precipitation agent at a flow rate ratio of 1.9, and a total flow rate resulting in a residence time of 8 hours. The aqueous transition metal solution contained Ni, Co and Mn at a molar ratio of 6:2:2 as sulfates each and a total transition metal concentration of 1.65 mol/kg. The alkaline precipitation agent consisted of 25 wt. % sodium hydroxide solution and 25 wt. % ammonia solution in a weight ratio of 25. The pH value was kept at 11.9 by separate feed of an aqueous sodium hydroxide solution. After stabilization of particle size the resulting suspension was removed continuously from the stirred vessel. The mixed transition metal (TM) oxyhydroxide precursor was obtained by filtration of the resulting suspension, washing with distilled water, drying at 120° C. in air and sieving.
I.2. Manufacture of Cathode Active Materials
C-CAM.1 (Comparative): The mixed transition metal oxyhydroxide precursor obtained according to I.1 was mixed with Al2O3 (average particle diameter 6 nm) and LiOH monohydrate to obtain a concentration of 0.3 mole-% Al relative to Ni+Co+Mn+Al and a Li/(TM+Al) molar ratio of 1.03. The mixture was heated to 885° C. and kept for 8 hours in a forced flow of oxygen to obtain the electrode active material C-CAM 1.
D50=9.5 μm determined using the technique of laser diffraction in a Mastersize 3000 instrument from Malvern Instruments. The Al-content was determined by ICP analytics and corresponded to 820 ppm. Residual moisture at 250° C. was determined to be 300 ppm.
CAM.2 (inventive): A fluidized bed reactor with external heating jacket is charged with 100 g of C-CAM.1, and at an average pressure of 1030 mbar, C-CAM.1 is fluidized. The fluidized bed reactor is heated to 180° C. and kept at 180° C. for 3 h.
Step (b.1): Trimethylaluminum (TMA) in the gaseous state is introduced into the fluidized bed reactor through a filter plate by opening a valve to a precursor reservoir that contained TMA in liquid form and that is kept at 50° C. The TMA is diluted with nitrogen as carrier gas. The gas flow of TMA and N2 is 10 sccm. After a reaction period of 210 seconds non-reacted TMA is removed through the nitrogen stream, and the reactor is purged with nitrogen for 15 minutes with a flow of 30 sccm.
Step (c.1): Then, the pressure is set to 1030 mbar. Hydrogen fluoride in the gaseous state is introduced into the fluidized bed reactor by opening a valve to a reservoir that contained liquid HF kept at 24° C., flow: 10 sccm. After a reaction period of 120 seconds non-reacted HF is removed through a nitrogen stream, and the reactor was purged with nitrogen, 15 minutes at 30 sccm.
The above treatment with TMA and HF including the nitrogen purging is repeated 3 times.
Inventive coated oxide material CAM.2 is obtained.
| Number | Date | Country | Kind |
|---|---|---|---|
| 18193633.7 | Sep 2018 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2019/073204 | 8/30/2019 | WO | 00 |
