Electrode active material, its manufacture and use

Abstract

The present invention is related to an electrode active material for a lithium-ion battery of general formula (I): Li.sub.1+x(Ni.sub.aCo.sub.bMn.sub.cM.sub.d).sub.1−xO.sub.2 wherein x is in the range of from zero to 0.1, a is in the range of from 0.1 to 0.5, b is in the range of from 0.4 to 0.9, c is in the range of from zero to 0.3, d is in the range of from zero to 0.1, M is selected from Al, B, Mg, W, Mo, Ti, Si and Zr, with a+b+c+d=1 and a>c. In addition, the present invention is related to a method of manufacture of electrode active materials and to their use.

Claims

1. An electrode active material of formula (I):
Li.sub.1+x(Ni.sub.aCo.sub.bMn.sub.cM.sub.d).sub.1−xO.sub.2  (I) wherein x is in the range of from zero to 0.05, a is in the range of from 0.1 to 0.3, b is in the range of from 0.5 to 0.8, c is in the range of from zero to 0.15, d is in the range of from zero to below 0.05, M is selected from the group consisting of Al, B, Mg, W, Mo, Ti, Si and Zr, with a+b+c+d=1 and a>c and 0.01≤c+d≤0.15, and wherein Co and Ni are homogeneously distributed over the particle diameter of the respective electrode active materials.

2. The electrode active material according to claim 1, having an average secondary particle diameter (D50) in the range of from 5 to 20 μm.

3. The electrode active material according claim 1, wherein a volume of the crystallographic unit cell of partially delithiated material according to formula (II)
(Li.sub.1+x).sub.y(Ni.sub.aCo.sub.bMn.sub.cM.sub.d).sub.1−xO.sub.2  (II) is at most 1 percent smaller than a volume of the crystallographic unit cell of the respective fully lithiated material, with y fulfilling the condition that y.Math.(1+x) is in the range of from 0.35 to 1.

4. An electrode comprising a current collector and (A) at least one electrode active material according to claim 1, (B) carbon in electrically conductive form, (C) a binder, and (D) optionally, a solid electrolyte.

5. The electrode according to claim 4, comprising: (A) 50 to 100% by weight of the electrode active material according to claim 1; (B) 0 to 5% by weight of carbon in electrically conductive form; (C) 0 to 5% by weight of the binder; and, (D) optionally, a solid electrolyte, the weight percentages referring to the sum of (A)+(B)+(C)+(D).

6. A process for making an electrode active material according to claim 1, the process comprising: (a) manufacturing a particulate precursor by co-precipitation of hydroxides or carbonates of Ni, Co and, optionally, Mn and, optionally, M; (b) mixing the particulate precursor with a source of lithium to obtain a mixture; and (C) calcining the mixture obtained in (b).

Description

EXAMPLE 1: Li.SUB.1.03.(Ni.SUB.0.3.Co.SUB.0.6.Mn.SUB.0.1.).SUB.0.97.O.SUB.2

(1) Synthesis of Mixed Metal Hydroxide Precursor:

(2) The mixed metal hydroxide precursor material was made by simultaneous feed of aqueous transition metal sulfate solution and an alkaline precipitation agent into a stirred tank reactor, at a flow rate ratio of 1.8, and a total flow rate resulting in a residence time of 12 hours. The transition metal sulfate solution contained Ni, Co, and Mn in a molar ratio of 3:6:1 and a total transition metal concentration of 1.65 mol/kg. The alkaline precipitation agent consisted of an aqueous 25 wt. % solution of sodium hydroxide and a 25 wt. % ammonia solution in a weight ratio of 8.5. The pH value was kept constant at 12.0 by additional feed of aqueous sodium hydroxide solution. The mixed metal hydroxide precursor was obtained by filtration of the continuously overflowing slurry from the reactor, washing with distilled water, drying at 120° C. in air over a period of 12 hours, and sieving.

(3) Synthesis of Inventive Electrode Active Material CAM.1:

(4) The mixed metal hydroxide precursor obtained according to the description above was mixed with Li.sub.2CO.sub.3 to obtain a molar ratio of Li/(Ni+Co+Mn)=1.03. The mixture was heated in a forced flow of air with the following heating profile: heating rate 3K/min, 4 hours at 350° C., 4 hours at 675° C., 6 hours at 900° C., natural cooling to ambient temperature. Inventive electrode active material CAM.1 was obtained.

(5) Electrode Preparation:

(6) Electrodes were prepared by slurry casting onto Al foil (20 μm, Nippon) using a KTF-S roll-to-roll coater (Mathis AG). Slurries were obtained by dispersing cathode material (94 wt.-%), Super C65 (1 wt.-%, Timcal) and SFG6L (2 wt.-%, Timcal) conductive carbon additives as well as Solef® 5130 PVdF binder (3 wt.-%, Solvay) in 1-ethyl-2-pyrrolidone (NEP).

(7) Characterization:

(8) Electrochemical characterization was conducted at 25° C. on coin-type half cells. The cells were assembled inside an Ar-filled glovebox (MBraun) by stacking cathode, glass microfiber separator (GF/D, GE Healthcare Life Sciences, Whatman), and lithium foil anode (Rockwood Lithium Inc.) of diameters 13, 17 and 13 mm, respectively, using 250 μL of either electrolyte ELY.1 or ELY.2. The areal loadings were approx. 2.0 mAh/cm.sup.2 at C/10 and an upper cut-off voltage of 4.3 V.

(9) For in situ XRD, pouch-type cells were assembled in a dry room by stacking cathode (20 mm×40 mm), Celgard 2500 polypropylene separator (30 mm×50 mm) and lithium foil anode (24 mm×44 mm) using 250 μL of ELY.1. Prior to XRD, the electrodes were galvanostatically cycled in the voltage range of 3.0 to 4.3 V for 3 cycles. Then, the cells were inserted into the diffractometer and charged/discharged at C/10 for 1 cycle during the measurement. Constant voltage steps at the cut-off voltages were applied for 1 h to allow for thermodynamic equilibration of the electrode materials. 2D diffraction images were collected in transmission geometry with an exposure time of 90 s. The intensity of two consecutive images was added up and then integrated to obtain 1D patterns for further evaluation, resulting in a time resolution of 180 s. Data analysis was performed by Rietveld refinement using the software TOPAS-Academic version 5. The instrumental resolution function was determined from an annealed CeO.sub.2 sample and described by means of a (Thompson-Cox-Hastings) pseudo-Voigt profile function. The analysis comprised refinement of the lattice parameters a and c as well as the atomic coordinate z of the oxygen position. Broadening effects (apparent crystallite size, microstrain etc.) were accounted for by convolution-based profile fitting, as implemented in TOPAS. This approach is equivalent to the Double-Voigt method described by Balzar et al. and is based on the integral breadths of the diffraction lines. Background refinement was made using a 10-term Chebyshev polynomial function. Zero-point correction (by Norby) was used to correct for sample displacement errors of both the cathode material and Al current collector.

EXAMPLE 2 (Li.SUB.1.03.(Ni.SUB.0.2.Co.SUB.0.7.Mn.SUB.0.1.).SUB.0.97.O.SUB.2.)

(10) Synthesis of Mixed Metal Hydroxide Precursor:

(11) The mixed metal hydroxide precursor material was made by simultaneous feed of aqueous transition metal solution and an alkaline precipitation agent into a stirred tank reactor, at a flow rate ratio of 1.8, and a total flow rate resulting in a residence time of 12 hours. The transition metal solution contained Ni, Co, and Mn at a molar ratio of 2:7:1 and a total transition metal concentration of 1.65 mol/kg. The alkaline precipitation agent consisted of an aqueous 25 wt. % solution of sodium hydroxide and a 25 wt. % ammonia solution in a weight ratio of 8.5:1. The pH value was kept constant at 12.0 by an additional feed of aqueous sodium hydroxide solution. The mixed metal hydroxide precursor was obtained by filtration of the continuously overflowing suspension from the reactor, washing with distilled water, drying at 120° C. in air over a period of 12 hours and sieving.

(12) Synthesis of Inventive Electrode Active Material CAM.2:

(13) The mixed metal hydroxide precursor obtained according to the description above was mixed with Li.sub.2CO.sub.3 to obtain a molar ratio of Li/(Ni+Co+Mn)=1.03. The mixture was heated in a forced flow of ambient air with the following heating profile: heating rate 3 K/min, 4 hours at 350° C., 4 hours at 675° C., 6 hours at 900° C., natural cooling. Inventive electrode active material CAM.2 was obtained. Electrodes were prepared and tested analogously to Example 1.

COMPARATIVE EXAMPLE 3 (NCM523)

(14) Synthesis of Mixed Metal Hydroxide Precursor:

(15) A mixed metal hydroxide precursor according to the description above, but with the following composition: (Ni.sub.0.5Co.sub.0.2Mn.sub.0.3)(OH).sub.2.

(16) Synthesis of Lithiated Transition Metal Oxide:

(17) The mixed metal hydroxide precursor was mixed with Li.sub.2CO.sub.3 to obtain a molar ratio of Li/(Ni+Co+Mn)=1.08. The mixture was heated in a forced flow of ambient air with the following heating profile: heating rate 2.5 K/min, 4.8 hours at 350° C., 6 hours at 650° C., 7.2 hours at 900° C., cooling with 1 K/min. C-CAM.3 was obtained.

(18) Electrode Preparation

(19) Electrodes were prepared analogously to Example 1, but with different slurry composition: Slurries were obtained by dispersing cathode material (93 wt.-%), Super C65 (1.5 wt.-%, Timcal) and SFG6L (2.5 wt.-%, Timcal) conductive carbon additives as well as Solef® 5130 PVDF binder (3 wt.-%, Solvay) in N-ethylpyrrolidone. Tests: See Example 1.

COMPARATIVE EXAMPLE 4 (NCM111)

(20) Synthesis of Mixed Metal Hydroxide Precursor:

(21) A mixed metal hydroxide precursor according to the description above but with the following composition: (Ni.sub.0.33Co.sub.0.33Mn.sub.0.33)(OH).sub.2.

(22) Synthesis of Lithiated Transition Metal Oxide:

(23) The mixed metal hydroxide precursor was mixed with Li.sub.2CO.sub.3 to obtain a molar ratio of Li/(Ni+Co+Mn)=1.08. The mixture was heated in a forced flow of ambient air with the following heating profile: heating rate 2.5 K/min, 4.8 hours at 350° C., 6 hours at 650° C., 7.2 hours at 900° C., cooling with 1 K/min. C-CAM.4 was obtained. Electrodes were prepared and tested analogously to Example 1.

(24) The results are summarized in Table 1.

(25) TABLE-US-00001 TABLE 1 Test results of inventive electrode active materials CAM.1 CAM.2 Voltage Discharge Voltage Discharge (V) vs. capacity Volume (V) vs. capacity Volume Li [mA/g] change [%] Li [mA/g] change [%] 4.4 176 0.10 4.4 173 0.50 4.5 190 −0.35 4.5 188 0.01 C-CAM.3 C-CAM.4 Voltage Voltage (V) vs. Discharge Volume (V) vs. Discharge Volume Li capacity change [%] Li capacity change [%] 4.4 176 −2.20 4.4 165 −1.0 4.5 186 −2.80 4.5 177 −1.6

(26) The “volume change” given in the table refers to relative change in volume of the crystallographic unit cell when charging a cell with lithium anode and a cathode comprising the corresponding NCM material to a voltage of 4.4 V and 4.5 V, respectively. The “discharge capacity” is the specific discharge capacity for the corresponding material after charging the cell to the given voltage of 4.4 V and 4.5 V, respectively.

(27) The value of y was in the range of from 0.35 to 1 at 4.5 V.