V. Focused Fundamental Research - EERE - U.S. Department of ...

V.B.8 Characterization of New Cathode Materials and Studies of Li-Air Batteries (BNL, U. Mass)
Nam – U. Mass, Yang – BNL
developing new diagnostic tools to investigate battery
materials both in situ and ex situ, and then applies these to
explain the relationships between structure and function
for new materials.
Connected with pump
Approach
1. In situ XAS and XRD studies of new electrode
materials such as LiFe 1-y Mn y PO 4 and high capacity
Li 1.2 Ni 0.2 Mn 0.6 O 2 during electrochemical cycling to
carry out the diagnostic studies to improve the energy
density and cycle life of Li-ion batteries.
2. Soft XAS on the L-edges of Mn and Ni to distinguish
the difference between the surface and the bulk
structural changes caused by charge-discharge cycling
for new cathode materials such as Li 1.2 Ni 0.2 Mn 0.6 O 2 .
3. In situ and ex situ transmission electron microscopy
(TEM) coupled with selected area electron diffraction
(SAED) to study the structural changes of electrode
materials with high location specification and spatial
resolution.
4. Electrochemical studies of GDE for Li-air batteries.
5. Improve the performance of the GDE by surface
modification.
6. Design and synthesis of new electrolyte system with
capability to dissolve Li 2 O and Li 2 O 2 , and/or high
solubility of O 2 for Li-air batteries.
Results
Continued the in situ x-ray absorption and time
resolved XRD studies of G2 and G3 cathode materials
during heating
A new synchrotron based in situ XRD technique
shown in Figure V - 40 for studying the structural changes of
cathode materials of Li-ion batteries during chemical
lithium extraction in a NO 2 BF 4 /CH 3 CN solution has been
developed. This new technique was used to investigate the
phase transitions of LiFePO 4
As shown from Figure V - 41, taking the advantage of the
high resolution linear position sensitive silicon detector,
the reflections from LiFePO 4 and FePO 4 can be clearly
distinguished and identified. The changes of peak intensity
as a function of oxidation reaction time (about 48 minutes
total) or XRD scan number (total 50 scans) are plotted in
Figure V - 41b. The intensity of pattern corresponds to the
color scale (in the left). With increasing reaction time, the
peak intensities for FePO 4 increase while those for
LiFePO 4 .decrease. The formation of second phase FePO 4
can be observed at scan 4, indicating a short time (about 4
minutes) was needed for the newly formed FePO 4 phase to
grow enough crystal size to be detected by XRD. This is
quite different than the in situ XRD results using
electrochemical delithiation, where the appearance of
FePO 4 takes a much longer time.
Figure V - 40: The schematic of experimental set-up for in situ XRD studies
during chemical lithium extraction
Intensity(a.u.)
Intensity
Intensity(a.u.)
127000
0
NO 2 BF 4 /CH 3 CN solution
LiFePO 4 powder
Cotton
X ray beam path
Connected with waste container
Reaction: LiFePO 4
+ NO 2
BF
---> 4 FePO 4 +LiBF 4 +NO 2
LiFePO 4
*
background
(020)
FePO 4
(020)
(011)
(011)
*
*
(120)
*
(210)
*
(111)
(101)
(111)
(021)
a =6.000(6)
A
b =10.313(2)
c =4.691(0)
Time (min)
(021)
(121)
0
48
(200)
o
A o Ao
(031)
a =5.788(9)
A o b =9.816(0)
A o
c =4.783(9)
A o
(121)
(200)
(031)
(131)
(b)
8 1 0 1 2 1 4 1 6 1 8
2
=0.774
.7748 A)
Figure V - 41: XRD patterns during in situ chemical lithium extraction of
LiFePO4: (a) XRD pattern for LiFePO4 at the beginning of reaction; (b)
contour plot of peak intensities as a function of reaction time. (c) XRD
pattern for final FePO4 at the end of reaction.
In collaboration with Prof. Hong Li and his research
group at Institute of Physics, Chinese Academy of
Sciences, a comparative study of the structural changes
between LiMn 0.4 Fe 0.6 PO 4 cathode material samples with
and without mesoporous structure during electrochemical
cycling has been carried out using in situ and ex situ XRD
(Figure V - 42). The phase transformation behaviours are
quite different in these two samples. As shown in Figure V
- 43, the structure of the mesoporou sample changed back
to the original phase during first discharge with a high
o
*
*
(211)
(a)
(c)
(131)
(211)
Energy Storage R &D 504 FY 2011 Annual Progress Report