Process For Precipitating A Mixed Hydroxide

Abstract

Disclosed herein is a process for precipitating a mixed hydroxide of TM where TM includes Ni, at least one of Co and Mn, and, optionally, one of Al, Mg, Zr or Ti from an aqueous solution of salts of such transition metals or of Al or of Mg. The process is carried out in a stirred vessel and includes the step of introducing a 10 to 40% by weight aqueous solution of ammonia and an aqueous solution of transition metal salts through at least two inlets into the stirred vessel. An aqueous solution of alkali metal hydroxide is added separately from the at least two inlets.

Claims

1. A process for precipitating a mixed hydroxide of TM wherein TM comprises Ni and at least one selected from the group consisting of Co and Mn and, optionally, at least one selected from the group consisting of Al, Mg, Zr and Ti from an aqueous solution of salts of such transition metals or of Al or of Mg, wherein the process is carried out in a stirred vessel and comprises the step of introducing a 1 to 40% by weight aqueous solution of ammonia and an aqueous solution of transition metal salts through at least two inlets into said stirred vessel, wherein an aqueous solution of alkali metal hydroxide is introduced separately from the at least two inlets, and wherein at least two inlets are designed as a coaxial mixer that comprises two coaxially arranged pipes through which an aqueous solution of ammonia and an aqueous solution of transition metal salts are introduced into said stirred vessel.

2. The process according to claim 1, wherein the aqueous solutions of transition metal salts and of ammonia are introduced below a liquid level in the stirred vessel.

3. The process according to claim 1, wherein the aqueous solutions of transition metal salts and of ammonia are introduced above a liquid level in the stirred vessel.

4. The process according to claim 1, wherein the solution of transition metal salts is introduced through the inner pipe of the coaxial mixer and the solution of ammonia is introduced through the outer pipe.

5. The process according to claim 1, wherein the aqueous solution of ammonia contains alkali metal hydroxide in a molar ratio to the metal ions that is lower than 1.8.

6. The process according to claim 1, wherein the stirred vessel is a continuous stirred tank reactor.

7. The process according to claim 1 wherein in certain intervals, the coaxial mixer is flushed with water to physically remove transition metal (oxy)hydroxide incrustations.

8. The process according to claim 1, wherein the aqueous solution of ammonia and aqueous solution of transition metal salts are introduced at a velocity in the range of from 0.01 to 10 m/s.

9. The process according to claim 1, wherein TM contains metals according to formula (I)
Ni.sub.aM.sup.1.sub.bMn.sub.c  (I) where the variables are each defined as follows: M.sup.1 is Co or a combination of Co and at least one metal selected from the group consisting of Ti, Zr, Al and Mg, a is in the range from 0.15 to 0.95, b is in the range from zero to 0.35, c is in the range from zero to 0.8, and a+b+c=1.0 and at least one of b and c is greater than zero.

10-13. (canceled)

Description

[0158] Brief Description of the Drawing, FIG. 1:

[0159] A: Stirred vessel

[0160] B: Stirrer

[0161] C: Engine for stirrer

[0162] D: Baffles

[0163] E: Wall of outer pipe of coaxial nozzle containing NH.sub.3 solution

[0164] F: Wall of inner pipe of coaxial nozzle containing metal sulfate solution

[0165] G: Wall of pipe for NaOH solution

[0166] Brief Description of the Drawing, FIG. 2:

[0167] A: Stirred vessel

[0168] B: Stirrer

[0169] C: Engine for stirrer

[0170] D: Baffles

[0171] E: Wall of pipe for NH.sub.3 solution

[0172] F: Wall of pipe metal sulfate solution

[0173] G: Wall of pipe for NaOH solution

WORKING EXAMPLES

General Remarks

[0174] The nickel concentrations of precursors were analyzed by inductively coupled plasma optical emission spectrometry (ICP-OES) after dissolving the samples in concentrated hydrochloric acid.

[0175] To determine form factor and axis ratio of samples, both properties were first determined for at least 50 individual particles of each sample and then averaged.

[0176] The form factor of the individual particles was calculated from the perimeter and area determined from top view SEM images:

Form factor=(4π.Math.area)/(perimeter).sup.2

[0177] While, a perfect sphere would possess a form factor of 1.0, any deviation from perfect sphericity lead to form factors<1.0

[0178] To determine the axis ratio of the bounding box of a single particle, the smallest possible, rectangular bounding box is set around the top view SEM image of a particle. The axis ratio is calculated from the length of the two sides a.sub.1 and a.sub.2 (with a.sub.1≥a.sub.2) by: axis ratio of the bounding box=a.sub.1/a.sub.2.

[0179] While, a perfect sphere would possess an axis ratio of the bounding box of 1.0, all deviations from perfect sphericity lead to an axis ratio>1.0.

[0180] The lateral crystallite size as well as the transition probability P.sub.x of C19 stacking faults, the transition probability P.sub.y of 3R stacking faults and the transition probability car P.sub.car of interstratification of water or carbon dioxide were determined on the basis of X-ray diffraction. The diffracted peak width was fitted by using DIFFRAC.TOPAS V6 software (Bruker AXS GmbH. Instrumental broadening was considered during the peak fitting, leading to a separation of the instrumental from the sample broadening. The sample contribution is determined by using a single Lorentzian profile function that is defined by the following equation:

[00001]$\beta =\frac{\lambda }{L\cos \theta }$

[0181] I. Manufacture of the Inventive Precursors and of Comparative Precursors

[0182] I.1 Manufacture of Inventive Precursor TM-OH.1:

[0183] The example was carried out in a 2.4 L stirred vessel equipped with baffles and a cross-arm stirrer, with a coaxial mixer and a separate dosing tube for NaOH separated by 4 cm, see FIG. 1, in the context of the working examples also referred to as “Vessel 1”. Vessel 1 had a constant nitrogen overflow during all reactions. The coaxial mixer as well as the separate dosing tube for NaOH were located in the vessel so that the outlets were approximately 5 cm below the liquid level. The coaxial mixer consisted of two coaxially arranged pipes made of stainless steel. The inner and outer diameter of the inner circular pipe was 1.1 mm and 1.6 mm, respectively. The inner and outer diameter of the outer circular pipe was 2 mm and 4 mm, respectively. The separate dosing tube had an outer diameter of 6 mm, an inner diameter of 2 mm.

[0184] Vessel 1 was charged with 2 I of deionized water and the temperature of the vessel was set to 55° C. The stirrer element was activated and constantly operated at 1000 rpm (average input ˜4.5 W/l). An aqueous solution of NiSO.sub.4, CoSO.sub.4 and MnSO.sub.4 (molar ratio 91:4.5:4.5, total transition metal concentration: 1.65 mol/kg), aqueous sodium hydroxide (25 wt % NaOH) and aqueous ammonia solution (25 wt % ammonia) were simultaneously introduced into the vessel. The agueous transition metal solution was introduced via the inner pipe of the coaxial mixer while the aqueous ammonia solution was introduced via the outer pipe of the coaxial mixer. The aqueous sodium hydroxide solution was introduced through the separate dosing tube t.sub.1. The distance between the outlets of the two coaxially arranged pipes was in the range of 5 mm.

[0185] The molar ratio between ammonia and transition metal was adjusted to 0.25. The sum of volume flows was set to adjust the mean residence time to 5 hours. The flow rate of the NaOH solution was adjusted by a pH regulation circuit to keep the pH value in the stirred vessel at a constant value of 12.0. The apparatus was operated continuously keeping the liquid level in the vessel constant. A mixed hydroxide of Ni, Co and Mn was collected via free overflow from the vessel. The resulting slurry contained about 120 g/l mixed hydroxide of Ni, Co and Mn. The slurry was washed with deionized water and an aqueous solution of sodium hydroxide (1 kg of 25 wt % aqueous sodium hydroxide solution per kg of solid hydroxide), filtered and dried at 120° C. overnight to obtain the inventive precursor TM-OH.1. TM-OH.1 had an average particle diameter (D50) of 12.0 μm, a value of (D90-D10)/D50 of 1.40, a tap density of 1.76 g/l and a BET surface of 26.4 m.sup.2/g.

[0186] I.2 Manufacture of Comparative Precursor TM-OH.2:

[0187] The example was carried out in a 2.4 L stirred vessel equipped with baffles and a cross-arm stirrer, and three dosing tubes, one for an aqueous solution of NaOH, one for ammonia solution and one for the metal sulfate solution, see FIG. 2. The feed for the metal sulfate solution was separated from both other tubes by 8 cm each, while the tube for ammonia was separated by 2.5 cm from the tube for the NaOH solution. All tubes had an outer diameter of 6 mm, an inner diameter of 2 mm and were located in the vessel so that the corresponding outlet was approximately 5 cm below the liquid level. In the context of said working examples this vessel is also referred to as “vessel 2”. Vessel 2 had a constant nitrogen overflow during all reactions.

[0188] Vessel 2 was charged with 2 I of deionized water and the temperature of the vessel was set to 55° C. The stirrer element was activated and constantly operated at 1000 rpm (average input ˜4.5 W/l). An aqueous solution of NiSO.sub.4, CoSO.sub.4 and MnSO.sub.4 (molar ratio 91:4.5:4.5, total transition metal concentration: 1.65 mol/kg), aqueous sodium hydroxide (25 wt % NaOH) and aqueous ammonia solution (25 wt % ammonia) were simultaneously introduced into the vessel by the corresponding tube.

[0189] The molar ratio between ammonia and transition metal was adjusted to 0.25. The sum of volume flows was set to adjust the mean residence time to 5 hours. The flow rate of the NaOH solution was adjusted by a pH regulation circuit to keep the pH value in the stirred vessel at a constant value of 12.1. The apparatus was operated continuously keeping the liquid level in the vessel constant. A mixed hydroxide of Ni, Co and Mn was collected via free overflow from the vessel. The resulting slurry contained about 120 g/l mixed hydroxide of Ni, Co and Mn. The slurry was washed with deionized water and an aqueous solution of sodium hydroxide (1 kg of 25 wt % aqueous sodium hydroxide solution per kg of solid hydroxide), filtered and dried at 120° C. overnight to obtain the comparative precursor C-TM-OH.2. C-TM-OH.2 had an average particle diameter (D50) of 10.6 μm, a value of (D90-D10)/D50 of 1.35, a tap density of 1.92 g/l and a BET surface of 30.7 m.sup.2/g.

[0190] SEM images of TM-OH.1 and C-TM.OH.2 are disclosed in FIG. 3.

[0191] Powder X-ray Diffraction (PXRD) data was collected using a laboratory diffractometer (D8 Discover, Bruker AXS GmbH, Karlsruhe). The instrument was set up with a Molybdenum X-ray tube. The characteristic K-alpha radiation was monochromatized using a bent Germanium Johansson type primary monochromator. Data was collected in the Bragg-Brentano reflection geometry in a 2θ range from 5.0 to 50°, applying a step size of 0.019°. A LYNXEYE area detector was utilized to collect the scattered X-ray signal.

[0192] For XRD measurements, the precursors were ground using an IKA Tube Mill and an MT40.100 disposable grinding chamber. The powder was placed in a sample holder and flattened using a glass plate.

[0193] Rietveld refinement analyses of the microstructures of the precursor materials were performed using DIFFRAC.TOPAS V6 software (Bruker AXS GmbH).

[0194] XRD patterns of TM-OH.1 and C-TM.OH.2 are disclosed in FIGS. 5 and 5. It should be noted that, e.g., the reflections at 2Θ of about 15 and 17.5° are different in height.

TABLE-US-00001 TABLE 1 Overview over the different precursor properties Form Axis ratio P.sub.x P.sub.y P.sub.car Lateral crystallite precursor factor BB [%] [%] [%] size [nm] TM-OH.1 0.88 1.26 0.11 0.07 0.08 62 C-TM-OH.2 0.88 1.27 0.12 0.06 0.10 14

[0195] Form factor and axis ratio were determined from the top view images of the particles shown in FIG. 3. The transition probabilities P.sub.x, P.sub.y and P.sub.car and the lateral crystallite size were determined from the corresponding X-ray diffraction patterns shown in FIG. 4 and FIG. 5.

[0196] II. Manufacture of Cathode Active Materials, and Electrode Manufacture

[0197] II.1 Manufacture of Inventive Cathode Active Material CAM.1 and the Comparative Cathode Active Material C-CAM.2:

[0198] To obtain cathode active materials, the respective precursors were mixed with LiOH.Math.H.sub.2O, Al.sub.2O.sub.3 and Zr(OH).sub.4 in molar ratio of Li:(Ni+Co+Mn) of 1.01:1, Al Li:(Ni+Co+Mn) of 0.02:1, Zr Li:(Ni+Co+Mn) of 0.0025:1, poured into a alumina crucible and heated at 350° C. for 4 hours and 720° C. for 6 hours under oxygen atmosphere (10 exchanges/h) using a heating rate of 3° C./min. The resultant material was cooled to ambient temperature at a cooling rate of 10 ° C./min and subsequently sieved using a mesh size of 30 μm to obtain the inventive cathode active material CAM.1 from precursor TM-OH.1 and the comparative cathode active material C-CAM.2 from the comparative precursor C-TM-OH.2.

[0199] II.2 Manufacture of Electrodes and Testing

[0200] Electrode manufacture and Half-Cell Electrochemical measurements:

[0201] Electrodes contained 94% CAM, 3% carbon black (Super C65) and 3% binder (polyvinylidene fluoride, Solef 5130). Slurries were mixed in N-methyl-2-pyrrolidone and cast onto aluminum foil by doctor blade. After drying of the electrodes for 6 h at 105° C. in vacuo, circular electrodes were punched, weighed and dried at 120° C. under vacuum for 12 hours before entering in an Ar filled glove box.

[0202] Coin-type electrochemical cells, were assembled in an argon-filled glovebox. The positive 14 mm diameter (loading 8.0±0.5 mg cm.sup.−2) electrode was separated from the 0.58 mm thick Li foil by a glass fiber separator (Whatman GF/D). An amount of 95 μl of 1 M LiPF6 in ethylene carbonate (EC): ethylmethyl carbonate (EMC), 3:7 by weight, was used as the electrolyte. Cells were galvanostatically cycled at a Maccor 4000 battery cycler between 3.1 and 4.3 V at room temperature by applying the following C-rates:

TABLE-US-00002 TABLE 2 Electrochemical test procedure of the coin half cells. Charge Discharge Cycle 1 0.1 C 0.1 C Cycle 2-6 0.2 C + CV* 0.2 C Cycle 7 & 8 0.5 C + CV* 0.5 C Cycle 9 & 10 0.5 C + CV* 2.0 C Cycle 11 & 12 0.5 C + CV* 3.0 C Cycle 13 & 14 0.5 C + CV* 0.5 C Cycle 15 Resistance measurement Cycle 16-40 0.5 C + CV* 1.0 C Cycle 41 + 42 0.5 C + CV* 0.5 C Cycle 43 Resistance measurement Cycle 44-68 0.5 C + CV* 1.0 C

[0203] After charging at the listed C-rates, all charging steps except the first were finished by a constant voltage step (CV*) for 1 hour, or until the current reached 0.02 C.

[0204] During the resistance measurement (conducted every 25 cycles at 25° C.), the cell was charged at 0.2 C to reach 50% state of charge, relative to the previous discharge capacity. To equilibrate the cell, a 30 min open circuit step followed. Finally, a 2.5 C discharge current was applied for 30 s to measure the resistance. At the end of the current pulse, the cell was again equilibrated for 30 min in open circuit and further discharged at 0.2 C to 3 .0 V.

TABLE-US-00003 TABLE 3 Discharge capacity (DC) and coulombic efficiency (CE) of comparative cathode active material C-CAM.2 and inventive cathode active materials CAM.1. DC 1.sup.st cycle CE 1.sup.st DC 5.sup.th cycle DC 25.sup.th cycle DC 50.sup.th cycle CAM [mA .Math. h/g] cycle [mA .Math. h/g] [mA .Math. h/g] [m .Math. Ah/g] CAM.1 209 91.0% 199 175 162 C-CAM.2 199 88.3% 190 170 159