Sunday, April 20, 2008

Synthesizing Ultra-fine LiCoO2 by Glycine-nitrate Combustion Method

This paper was publish at International Meeting on Lithium Batteries, 18 - 23 Jun 2006, Biarritz, France.
In this paper, Glycine-Nitrate Combustion method, which is a self sustaining combustion process using metal nitrates as the oxidizer and glycine as the fuel has been used to obtain an ultra-fine and electrochemically active powder of LiCoO2.
Figure (a) shows very fine particle size of LiCoO2, which is less than 100nm. Figure (b) shows cyclic voltammogram of LiCoO2, scan at 10mV/min, within voltage range of 3.0 to 4.2 volt.

Thursday, April 17, 2008

Rate Discharge vs Particle Size of LiCoO2

This paper was published at 23rd Regional Conference on Solid State Science and Technology 2007 (RCSSST 2007), 27-29 Nov 2007, HYATT REGENCY HOTEL JOHOR BAHRU, MALAYSIA
Figure (a)

Figure (b)

Figure (a) shows Scaning Electron Micrograph (SEM) image of the LiCoO2 crushing using Planetery Ball Milling process in our Laboratory. The Figure shows the changing of particle at various crushing time. The particle size of the LiCoO2 decreased when milling time increased. The longer of crushing time, the smaller particle size. It has a limiting crushing time, longer crushing time might be changing the material phase.

Figure (b) shows correlation between particle size and rate discharge performance of LiCoO2. It is found that the discharge capacity of the fresh sample (0 hour) drastically decreased close to 50% when discharged at 5 mA discharge current. Conversely, when using the small particle size sample, the recovery capacity maintained at 50%, even though the discharge current used is 20mA, which is about 4 times higher than fresh sample (0 hour milling). These results show that particle size plays an important role in synthesizing high power density cathode materials. The increasing in power density for the small particle size is due to the shorten of diffusion path length for lithium ions in the cathode material and a large contact area with conductive additives such as carbon as well as electrolyte. The path length concept is illustrated as figure (c).

Figure (c)

High magnification of TEM image of LiCoO2

This paper was published at The 18th International Conference on Solid State Ionics, 1-6 July, 2007, Shanghai International Convention Centre, Shanghai, CHINA.



The Figure (a) above shows high magnification Transmission Electron Microscope (TEM) image of the LiCoO2 synthesized in our laboratory. Particle size of the focus image is 35 nm. The focus image is a single crystal particle, where the fringes can be observed in the TEM image. This fringes are representing interlayer dispacing of the lattice structure. The distance between fringes is shown in the subfigure, which is 1.4 nm or 14Å.
Calculation using XRD data show as follows;

Bragg Law, d = n(lambda)/ (2 x Sin(theta))
= 1.5406/ (2 x Sin(9.38))
= 4.7258Å
length of the c axis, c = 3d
= 3 x 4.7258Å
= 14.1Å or 1.41 nm

Result above shows the agreement between TEM measurement data and lattice size calculated using XRD data.
Figure (b) shows the lattice size for LiCoO2 as publish in Nature, (2003) Vol. 2, pg. 464-467

Cauliflower-like Nano Structure

This paper was published at 6th ASEAN Microscopy Conference, 10-12 Dec 2007, Impiana Cherating Hotel, Pahang.

Figure shows the morphology of Li[Ni1/3Co1/3Mn1/3]O2 powder synthesize in our laboratory. The particle size was ranging from 50 nm to 300 nm and the particle surface was rough with spot like pimple. The type of structure is illustrated as cauliflower-like nano structure. This type of structure will produce high specific surface area per volume, which is an important characteristic in synthesizing high power density cathode materials.