METHOD FOR COVERING PARTICLES, ESPECIALLY A BATTERY ELECTRODE MATERIAL PARTICLES, AND PARTICLES OBTAINED WITH SUCH METHOD AND A BATTERY COMPRISING SUCH PARTICLE

Abstract

Described here is a powder comprising a plurality of lithium-containing particles having a dry, uniform protective layer, wherein the protective layer of the particles is obtained by a sequential vapor phase reaction or adsorption process. Also described is a battery comprising an anode layer and a cathode layer, wherein the cathode layer comprises lithium metal oxide or a lithium metal phosphate, wherein the metal comprises at least one of Nickel, Manganese, Cobalt, Iron, Titanium, and/or Manganese, wherein the cathode particles have a dry, uniform protective layer, and wherein the anode layer comprises lithium titanium oxide particles.

Claims

1-22. (canceled)

23. A powder comprising a plurality of lithium-containing particles having a diameter of 60 μm or less; a uniform alumina protective layer disposed over the lithium-containing particles.

24. A battery comprising an electrode wherein the electrode comprises the lithium-containing particles of claim 23.

25. The powder of claim 23 wherein the lithium-containing particles having a diameter in the range of 10 nm to 500 nm.

25. The powder of claim 23 wherein the lithium-containing particles having a diameter in the range of 10 nm to 100 nm.

26. The powder of claim 23 wherein the lithium-containing particles comprise LiMn.sub.2O.sub.4, LiCoO.sub.2 or LiNiO.sub.2.

27. The powder of claim 23 wherein the lithium-containing particles comprise LiFePO.sub.4.

28. The powder of claim 23 wherein the lithium-containing particles comprise LiTiOi.sub.2.

29. The powder of claim 23 wherein the lithium-containing particles comprise LiMn.sub.2O.sub.4, and further comprising Mg or Ni.

30. The battery of claim 24 comprising particles of LiFe.sub.xTi.sub.yMn.sub.2-x-yO.sub.4 where 0<y<0.3.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0024] The accompanying drawings, which are incorporated into and form a part of the specification, illustrate one or more embodiments of the present invention and, together with the description, serve to explain the principles of the invention. The drawings are only for the purpose of illustrating one or more preferred embodiments of the invention and are not to be construed as limiting the invention. In the drawings:

[0025] FIG. 1 shows a schematic drawing of the experimental setup for the ALD-process (atomic layer deposition). It consists of a 26 mm internal diameter, 500 mm long glass reactor tube that is filled with LiMg.sub.0.05Ni.sub.0.45Mn.sub.1.5O.sub.4 nano-particles with a diameter of 10-50 nm. The reactor is placed on a shaker driven by two vibromotors that produce a low amplitude vibration at adjustable frequency to assist fluidization. The fluidizing gas is nitrogen. Each ALD-cycle consists of four process steps:

[0026] 1. Valve V1 is opened, so that part of the nitrogen is led through a bubbler containing the organo-metallic precursor and saturated with its vapor. This vapor adsorbs on the particle surface;
2. When the complete particle surface is covered with the precursor, V1 is closed and V2 is opened to flush the tubes with pure nitrogen. This prevents (undesired) reactions in the tubes;
3. V2 is closed and V3 opened to lead the gas through a bubbler containing water. The water vapor reacts with the organo-metal on the surface of the powder;
4. V2 is opened again and V3 closed to clear the tubes for the next cycle.

[0027] These steps are repeated until a sufficient number of cycles have been performed to achieve the desired thickness of the coating.

[0028] The variables that can be adapted in the ALD-process are the number of cycles, coating material, overall flow, reactant concentration, cycle times for precursor and water, vibration frequency, reaction temperature, etc. During the process the temperature, pressure difference and pressure fluctuations are recorded.

[0029] For the experiments described in this paper, only the fluidization part of the set-up has been used, i.e., gas without reactants for the fluidization, assisted by vibration. The gas flow was varied from 0 to 21/min. (velocities of 0-63 mm/s), and several vibration frequencies were used, ranging from 0-47 Hz. Higher gas velocities were not used because the particles started to be elutriated from the column.

[0030] Pressure fluctuations were measured at a frequency 20 of 400 Hz using piezo-electric pressure transducers, Kistler type 7261, at two heights in the column: 50 mm and 125 mm above the gas distributor. For titania particles, that were used in some experiments, the data from 125 mm are given here because of a blockage of the lower measuring point after some time; for the cathode particles the height of 50 mm was used due to the lower initial bed height. For the titania particles, the data from the higher and lower measuring point were comparable. The fluidization experiments were done at room temperature and atmospheric pressure.

[0031] Two types of particles were used: the first type is the LiMg.sub.0.05Ni.sub.0.45Mn.sub.1.5O.sub.4 cathode material, which was prepared by an auto-ignition method (described by Lafont et al.). FIG. 2 shows TEM (transmission electron microscope) pictures of this material. The particle dimensions observed in these TEM images are 20-100 nm. A (Brunauer-Emmett-Teller) BET-analysis rendered a surface of 6.4 m.sup.2/g, from which an equivalent diameter of 213 nm can be calculated. Laser diffraction showed a very wide particle size distribution, ranging from 40 nm or smaller (40 nm is the lower limit of the apparatus) to 60 μm (clusters). Combination of these measurements leads to the conclusion that the particles form clusters, and that part of the clusters are “hard” aggregates, with some necking between the primary particles. To make a comparison possible, also a more common type of nano-particles has been investigated: commercial titania particles. These particles have a diameter of 20-25 nm and a surface area of 90 m.sup.2/g (data from manufacturer Kerr-McGee Pigments). It is expected that it is a loose powder and at all aggregates in this powder are soft aggregates that break up easily.

[0032] FIG. 3 shows the relative bed expansion during the experiments. To calculate this, the minimum bed height as measured during all experiments, was taken as the initial bed height H.sub.0. This minimum was found when the bed was compacted at the highest vibration frequency. For these experiments, the vibration frequency was set to a fixed value, and the gas velocity adjusted. We started with the lowest frequency.

[0033] However, the experiments were also carried out with particles with a history of vibration, also at high frequencies; these particles are marked with an * in the figures. The graphs confirm that the initial bed height depends on the vibration frequency, at higher frequencies the particles are packed closer.

[0034] Visual observations of the fluidization behavior of the cathode particles suggest that at low gas velocities, there is some channeling. At higher velocities, the eruptions at the bed surface are more violent and appear to originate from (small) bubbles, although these are hard to distinguish since the powder is black. The vibrations have some influence: at high frequencies bubbles start to appear at lower gas velocities. The effect was not quantified due to aforementioned visibility problems. For the (white) titania powder it is easier to distinguish channels and bubbles. For each velocity and frequency, there is a certain part in the bottom of the bed that is not moving. Some large aggregates can be distinguished here and channeling occurs in between these aggregates. The height of this part decreases with gas velocity and vibration frequency. Above this bottom zone, the bed fluidizes with small bubbles. A memory effect could be noticed for both particle types, although it was stronger and lasted longer for the titania. The non-moving bottom zone was much smaller for particles with a history of vibration than for “fresh” particles. An explanation could be that part of the aggregates was broken up by the high frequencies, and only the very large (hard) aggregates remained. The bed expansion factor WHO reached a maximum value of 2.0 for the cathode particles and 1.63 for the titania particles. It was also found that when the vibration and gas flow are stopped, the bed does not return to its initial height, and even after several days it may still be expanded (H/H01, 4), showing that the aggregates are very loosely packed. The measured porosities for the cathode particles were in the range of 0.66-0.83, and for the titania it was 0.87-0.92.

[0035] FIGS. 4A and 4B show the standard deviation of the pressure signal during the experiments, which could provide information on the regime in which the fluidized bed is operating. The pressure fluctuations in the experiments with a high vibration frequency are determined mainly by the vibrations, the influence of the gas flow was minor. This was confirmed by the power spectrum, where high peaks occurred at the vibration frequency. When there is no vibration or vibration at a low frequency, there is a noticeable influence of the gas flow on the pressure fluctuations, as is observed in a regular gas-fluidized bed as well.

[0036] For the cathode particles, the sudden rise followed by a decrease in the fluctuations at high frequencies could indicate a transition from bubbling to turbulent regime. However, more data are necessary to confirm this and explain the mechanism. For the TiO.sub.2 this transition was not observed for the studied range of gas velocities. The data series from particles with a vibration history show that this history and the change in fluidization behavior it causes do not have a large influence on the pressure fluctuations.

[0037] FIG. 5 further shows SEM (scanning electron microscope) photographs of particles obtained according to the method of the present invention and wherein as a first reactant water was added for forming a hydroxide monolayer on the particles (LiMn.sub.2O.sub.4). Then, trimethylaluminiurn (TMA) was added to the fluidization gas so as to perform a reaction of said TMA with the hydroxide monolayer. Subsequently, a further addition of water was performed, and a first monolayer of alumina on said particles was obtained. This combination of steps was repeated until an alumina layer on said particles was obtained in a sufficient thickness and was very homogeneous. The layer turned out to have a thickness of about 2 nm and consisted (by means of EDX (energy dispersive x-ray) in a SEM) of aluminium oxide.

[0038] The FIG. 6 shows the results on cyclic behavior of repeatedly charging and discharging batteries made from the coated particles according to the invention and uncoated particles as a reference example. Both at low temperature (20° C.) and high temperature (60° C.) the capacity at fast and slow discharge and charge rate is much higher in the batteries containing the coated particles as cathode material. Also, the uncoated particles show a clear fading in capacity due to degradation of the cathode material.

[0039] Therefore, from the above example, it can be concluded that the method, according to the present invention, is a suitable way for providing a protective layer on nano-particles.