MIXED LITHIUM TRANSITION METAL OXIDE COATED WITH PYROGENICALLY PRODUCED ZIRCONIUM-CONTAINING OXIDES

Abstract

Process for producing a coated mixed lithium transition metal oxide, wherein a mixed lithium transition metal oxide and a pyrogenically produced zirconium dioxide and/or a pyrogenically produced mixed oxide comprising zirconium are subjected to dry mixing by means of an electric mixing unit having a specific electrical power of 0.05-1.5 kW per kg of the mixed lithium transition metal oxide; coated mixed lithium transition metal oxide obtainable by this process; cathode for a lithium battery and lithium battery comprising such coated particles.

Claims

1. A process for producing a coated mixed lithium transition metal oxide, the process comprising: dry mixing a mixed lithium transition metal oxide and a zirconium source which is at least one selected from the group consisting of a pyrogenically produced zirconium dioxide and a pyrogenically produced mixed oxide comprising zirconium, wherein the dry mixing is performed using an electric mixing unit having a specific electrical power of 0.05 to 1.5 kW per kg of the mixed lithium transition metal oxide.

2. The process of claim 1, wherein: the specific electrical power of the electric mixing unit is 0.1 to 1000 kW.

3. The process of claim 1, wherein: a volume of the electric mixing unit used is 0.1 L to 2.5 m.sup.3.

4. The process of claim 1, wherein: a speed of a mixing tool in the electric mixing unit is 5 to 30 m/s.

5. The process of claim 1 to, wherein: the zirconium source has a BET surface area of 5 to 200 m.sup.2/g.

6. The process of claim 1, wherein: the zirconium source is in the form of aggregated primary particles, the primary particles having a numerical mean diameter of 5 to 100 nm, as determined by transition electron microscopy (TEM).

7. The process of claim 1, wherein: the zirconium source has a mean particle diameter d.sub.50 of 10 to 150 nm, as determined by static light scattering (SLS).

8. The process of claim 1, wherein: the zirconium source has a particle size span (d.sub.90-d.sub.10)/d.sub.50 of 0.4 to 1.2, as determined by static light scattering (SLS).

9. The process of claim 1, wherein: the pyrogenically produced mixed oxide comprising zirconium further comprises lithium and optionally comprises at least one selected from the group consisting of lanthanum and aluminium.

10. The process of claim 1, wherein: the mixed lithium transition metal oxide is at least one selected from the group consisting of a lithium-cobalt oxide, a lithium-manganese oxide, a lithium-nickel-cobalt oxide, a lithium-nickel-manganese-cobalt oxide, a lithium-nickel-cobalt-aluminium oxide, and a lithium-nickel-manganese oxides, or a mixture thereof.

11. The process of claim 1, wherein: the zirconium source is present in an amount of 0.05% to 5% by weight, based on a total weight of the mixed lithium transition metal oxide and the zirconium source.

12. A coated mixed lithium transition metal oxide comprising a zirconium material which is at least one selected from the group consisting of a pyrogenically produced zirconium dioxide and a pyrogenically produced mixed oxide comprising zirconium, the zirconium material having a number average particle size d.sub.50 of 10 nm to 150 nm, and being present on thea surface of the mixed lithium transition metal oxide.

13. An active positive electrode material for a lithium battery comprising the coated mixed lithium transition metal oxide of claim 12.

14. A lithium battery comprising the coated mixed lithium transition metal oxide of claim 12.

15. (canceled)

Description

EXAMPLES

[0078] Starting Materials

[0079] Fumed ZrO.sub.2 with a specific surface area (BET) of 40-60 m.sup.2/g, was produced by flame spray pyrolysis according to Example 1 of WO 2009053232 A1.

[0080] Commercial “nano ZrO.sub.2” powder (particle size 20-30 nm) with BET surface area of ≥35 m.sup.2/g, was supplied by ChemPUR Feinchemikalien and Forschungsbedarf GmbH

[0081] Commercial mixed lithium nickel manganese cobalt oxide powder NMC (7-1.5-1.5) (Type PLB-H7) with a BET surface area of 0.30-0.60 m.sup.2/g, a medium particle diameter d.sub.50=10.6±2 μm (determined by static laser scattering method), was supplied by Linyi Gelon LIB Co.

[0082] Particle Size Distribution of Different ZrO.sub.2 Types

[0083] The samples of a fumed ZrO.sub.2 or a commercial “nano ZrO.sub.2” powder (5 wt %) were dispersed in the solution of sodium pyrophosphate (0.5 g/L) in distilled water and treated at 25° C. for 1 minute in an external ultrasonic bath (160 W).

[0084] FIG. 1 shows the particle size distribution of the fumed ZrO.sub.2 and FIG. 2 shows the particle size distribution of the “nano ZrO.sub.2”, analyzed by static laser diffraction method (SLS) using laser diffraction particle size analyzer (HORIBA LA-950). For fumed ZrO.sub.2, a mono-modally and very narrow particle size distribution was detected (d.sub.10=0.06014 μm, d.sub.50=0.07751 μm, d.sub.90=0.11406 μm, span=(d.sub.90-d.sub.10)/d.sub.50=0.7), while a wide spread bimodal distribution was detected for “nano ZrO.sub.2” of ChemPUR, showing large non-dispersed particles (d.sub.10=0.10769 μm, d.sub.50=3.16297 μm, d.sub.50=5.80804 μm, span=(d.sub.90-d.sub.10)/d.sub.50=1.8).

Example 1

[0085] The NMC-powder (217,8 g) was mixed with 2,2 g (1.0 wt %) of the fumed ZrO.sub.2-powder in a high intensity laboratory mixer (Somakon mixer MP-GL with a 0.5 L mixing unit) at first for 1 min at 500 rpm (specific electrical power: 350W/kg NMC) to homogeneously mix the two powders. Afterwards the mixing intensity was increased to 2000 rpm (specific electrical power: 800 W/kg NMC, tip-speed of the mixing tool in the mixing unit: 10 m/s) and the mixing was continued for 5 min to achieve the dry coating of the NMC particles by ZrO.sub.2.

[0086] The coated NMC particles showed a ZrO.sub.2-coating layer thickness of 10-200 nm, as determined by TEM analysis.

Comparative Example 1

[0087] The procedure of Example 1 was repeated exactly with the only difference, that “nano ZrO.sub.2” powder was used instead of fumed ZrO.sub.2.

[0088] Analysis of ZrO.sub.2-coated mixed lithium transition metal oxides by SEM-EDX FIG. 3 shows the SEM-EDX mapping of Zr (white) on ZrO.sub.2-coated NMC prepared by using fumed ZrO.sub.2 (Example 1), FIG. 4 shows the results of the analysis of NMC coated with “nano ZrO.sub.2” (Comparative Example 1). The axes of FIGS. 3 and 4 show: x axis=diameter of particles; the left y axis=volume in %, the right y axis=cumulative volume in %. NMC mixed oxide dry coated with fumed ZrO.sub.2, shows a full and homogeneous coverage of all NMC particles with ZrO.sub.2. No larger ZrO.sub.2 agglomerates were detected, showing a good dispersibility of nanostructured fumed ZrO.sub.2. Additionally, no free unattached ZrO.sub.2-particles next to the NMC particles were found, indicating the strong adhesion between coating and the substrate (NMC). In contrast, FIG. 5 shows that only the fine ZrO.sub.2-particles of “nano ZrO.sub.2” are attached to the surface of NMC particles. The larger ZrO.sub.2-particles are non-dispersed and are therefore unattached, located next to the NMC particles. As a result, the NMC particles are not fully covered by zirconium oxide.

[0089] Preparation of Electrodes

[0090] Electrodes for electrochemical measurements were prepared by blending 90 wt % NMC with 5 wt % of a polyvinylidene fluoride binder (PVDF 5130, manufacturer: Solef) and 5 wt % of a conductive carbon black (SUPER PLi, manufacturer: TIMCAL) under inert gas atmosphere. N-Methyl-2-pyrrolidone (NMP) was used as a solvent. The slurry was casted on aluminum foil and dried at 120° C. for 20 min on a heating plate under air. Afterwards, the electrode sheet was dried in a vacuum furnace at 120° C. for 2 h. Circular electrodes with a diameter of 12 mm were punched out of a larger piece and then flattened between 2 rollers with a pressure of 90 psi, and dried again in a vacuum furnace at 120° C. for 12 h to remove any residual water and NMP.

[0091] Assembly of Lithium Batteries

[0092] The lithium battery cells for the cycling tests were assembled as CR2032 type coin cells (MTI Corporation) in an argon-filled glovebox (GLOVEBOX SYSTEMTECHNIK GmbH). Lithium metal (ROCKWOOD LITHIUM GmbH) was used as the anode material. Celgard 2500 was used as the separator. 25 μL of a 1 M solution of LiPF.sub.6 in ethylene carbonate and ethyl methyl carbonate (50:50 wt/wt; SIGMA-ALDRICH) was used as an electrolyte. The cells were locked with a crimper (MTI).

[0093] Galvanostatic Cycling Tests

[0094] Galvanostatic cycle performance of the assembled lithium batteries was measured at 25° C. using a MACCOR battery cycler at cut-off voltage of 3.0-4.3 V. The C-rate (charge/discharge) was increased every four cycles, starting from 0.1 C/0.1 C (Charge/Discharge) to 0.3 C/0.3 C, 0.5 C/0.5 C, 1.0 C/1.0 C, 1.0 C/2.0 C and 1.0 C/4.0 C. Afterwards, the cell was cycled at 0.5 C/0.5 C for long term stability test. (0.5 C rate corresponds to current density of 0.7 mAh/cm.sup.2). For the calculation of the capacities and the specific currents, only the mass of the active material was considered. The results are presented in FIG. 5. The axes of FIG. 5 show: x axis=number of cycles; y axis=discharge capacity in mAh/g.

[0095] In FIG. 5, the cycling performance of NMC coated with fumed ZrO.sub.2 (line with triangles) is compared with the NMC coated with “nano ZrO.sub.2” (line with circles) and as a reference with the uncoated NMC (line with squares). It is clear from the results, that the fumed ZrO.sub.2 coating improves the stability and cycle life of NMC significantly. The NMC coated with fumed ZrO.sub.2 shows comparing with the other tested materials the highest discharge capacity over all cycles, both in the rate test at the beginning and in the long-term cycling test. It is remarkable that it also shows the higher initial specific discharge capacities at 0.1 C than the other samples. The cell with NMC coated with “nano ZrO.sub.2” shows a significantly worse cycling performance. For this material, the rate performance at a discharge rate of 4 C and the capacity retention in the long-term cycling test is even worse than the results for the uncoated NMC.