X-Ray Diffraction
XRD patterns of all samples are shown in Figure 4. The peaks correspond to hexagonal layered structure. There exists no extra peak representing phase impurity. From XRD patterns it can be observed that intensity ratios of the (003) and (104) lines are larger than 1.5 and splitting of the (006,012) and (018,110) lines are clearly observed. This implies a complete phase pure material without or less cation mixing. Splitting of (006,012) is more prominent when the calcinations temperature is 900°C. All the peaks were examined separately for a detailed study.
Figure 4: XRD Patterns for Samples Calcined under Different Conditions of Time and Temperatures
Peak intensities of plane (003) have increased linearly with an increase of time and temperature. Small peaks are observed between 20° and 25° which is a characteristic of superlattice ordering of Li, Ni, Co and Mn in the transition metal layers. (Refer to Figure 5) It may be also due to minor amount of Li2MnO3 monoclinic phase.
Figure 5: XRD Pattern Showing Increase in Peak Intensity of (003) Plane and Small Peaks Between 20°-25° Indicating a Superlattice Structure
Figure 6: EDS Analysis Showing all Transition Metal Present
Energy dispersive x-ray (EDS) analysis was conducted to identify the presence of transition metals in Li1+xMnaCobNicTidO2. It can be observed that all Mn, Co, Ni and Ti are present in samples synthesized under different conditions of time and temperatures
Scanning electron micrographs (SEM) of all samples are shown in Figure 7 through 8. All samples were examined before crushing and grinding and show agglomerated morphology. It can be observed that the particles are crystalline within a range of 150 nano meter to 1-2 microns. From the SEM observation it can be confirmed that the synthesized samples are composed of porous agglomerates consisting of submicron sized particles and agglomerate size is around 5-10 microns. Porous structures of this type should facilitate deep penetration of the electrolyte within the electrode material and submicron size particles will enhance lithium ion diffusion. These materials have the potential to provide high energy and power density for lithium ion batteries.
Figure 7: SEM micrograph showing morphology and crystal size under condition 1
Figure 8: SEM micrograph showing morphology and crystal size under condition 2
Electrochemical Characterization
Electrolyte used was 1.4 M LiPF6 in EC/EMC (1:3 v/v) and graphite was used as anode. 1g of active cathode material was used for each batch and was mixed with different high conductive carbonaceous materials.
Figure 9 shows a discharge profile at C/5 rate. It can be observed that a specific capacity of 170 mAh/g can be achieved. Figure 10 shows all discharge capacities at C/5 rate starting from forming at 40°C.
Figure 9: A Specific Capacity of 170 mAhg-1 with Excellent Cycleability at C/5 rate.
Figure 10: Specific Discharge Capacities with Excellent Cycleability at C/5 rate
 |
|
|
