Two phase reaction No significant solid solution region
Existence of solid solution regions Appearance of Intermediate phase
T(311)
T(121)
(311)
35.5
36.0
36.5
3. Soft X-ray absorption spectroscopy study of charged cathode materials
(bulk information) Fluorescent Electronic structural detector (surface information) information at the Electron yield surface (~ 50Å ) and in detector Charged ciffraction pattern
Incident X-rays
Al current collector Active material
Cu current collector Li foil
2
In situ cell
Synchrotron based X-ray diffraction and absorption spectroscopy during heating
0.5
0.0
0.0
7710
7720
7730
8320
8330
8340
8350
8360
Energy ( eV )
Three voltage plateaus at ~ 3.6, 4.2 and 4.7 V Redox reactions of Fe2+/Fe3+, Mn2+/Mn3+ and Co2+/Co3+. Voltage plateau over ~ 4.9V Mostly electrolyte decomposition. Electronic structural changes following the lithium extraction quite well to balance the electrical neutrality.
More charged state, more thermally unstable. Released oxygen causes safety problems (e.g., thermal runaway) by reacting with flammable electrolytes.
Using Synchrotron Based in situ X-ray Techniques and Transmission Electron Microscopy to Study Electrode Materials for Lithium Batteries
X. Q. Yang, K. W. Nam, X.J. Wang, Y.N. Zhou, H. S. Lee, O. Haas, L. Wu, and Y. Zhu Brookhaven National Lab. Upton, NY11973, USA K. Y. Chung and B. W. Cho Battery Research Center, Korea Institute of Science and Technology, Seoul 130-650, Korea Hong Li, Xuejie Huang and Liquan Chen Institute of Physics, Chinese Academy of Sciences, Beijing, China To be presented at the 4th Southern China Li-ion Battery Top Forum –CLTF2009 Shenzhen, China, May 25th, 2009
37.0
37.5
35.5
36.0
36.5
(121)
37.0
2 (=1.54)
2
4
5
In situ XAS of C-LiFe1/4Mn1/4Co1/4Ni1/4PO4 during first charge
Edge shift toward higher energy position increase in oxidation state
K. W. Nam, X. Q. Yang et al, Electrochemistry Communication, in press (2009).
6
Thermal stability study of layered cathode materials (safety related issue)
XAS setup
Monochromatic X-rays
In situ cell
Mylar sheet Bolt holes Gasket Separator X-ray window
IRef
IT
IO
Reference metal foil
In situ cell
Position sensitive detector (PSD)
3
In situ XRD of C-LiFe1/4Mn1/4Co1/4Ni1/4PO4 during first charge
Comparison with pure C-LiFePO4
H(121)
C-LiFePO4
H(311)
Phase1
C-LiMn1/4Fe1/4Co1/4Ni1/4PO4
Phase 2 Phase 3
Oxygen release When x= 0.5 (50% of SOC) in LixMO2
Oxygen release
Li0.5M(3.5+)O2 (layered, R-3m) Li0.5M(3.5+)1.0O2 (disordered spinel, Fd3m) ; no oxygen loss Li0.5M(3.5+)1.0O2 (disordered spinel, Fd3m) Li0.5M(2.5+)1.0O1.5 (rock salt, Fm3m) + 0.25 O2 ; oxygen release!!
7
Thermal stability of Li0.33NiO2 with electrolyte (as a reference)
- Li0.33NiO2
A good road map for the structural changes of nickel-based cathode materials during heating. Heating up to 450 oC
Combination of these techniques will clearly provide valuable information about thermal stability of various types of cathodes materials and help designing cathode materials with superior thermal abuse tolerance !!
Combining in situ synchrotron XAS and XRD techniques to do diagnostic studies of battery materials and components at or near operating conditions
X19A & X18B (XAS) and X14A & X18A (XRD) at National Synchrotron Light Source (NSLS) Ionization Detectors
0
20
40
60
80
100
120
-1
140
160
180
Capacity ( mAh g )
1.2
Cut-off voltage: ~ 5.0 V, C/7 rate
0.6
Before charge -1 22 mAhg -1 41 mAhg -1 60 mAhg -1 70 mAhg -1 79 mAhg -1 99 mAhg -1 137 mAh g -1 166 mAh g
Before charge -1 22 mAhg -1 31 mAhg -1 40 mAhg -1 48 mAhg -1 57 mAhg -1 75 mAhg -1 93 mAh g -1 163 mAh g
Voltage ( V vs. Li/Li )
+
Normalized intensity (a. u.)
Studies on thermal decomposition (thermal abuse tolerance) of cathode materials 1. Time-resolved XRD study of charged cathode materials
Samples in Heating capillary
Samples in capillary
Average structural information (long range order) during heating
Incident soft X-ray (500~1000eV)
the bulk (~ 3000Å ) in elemental-selective way during heating