Electronic and Ionic Transport in NCA and NMC Cathodes
-9
-
Prepared pure-phase polycrystals with controlled
residual porosity allowing electrochemical titration
Excluded typical electrode additives that interfere
with mechanistic determination
Used ion-blocking and electron-blocking cell
configurations to isolate electronic and ionic transport
Used both ac and dc-relaxation techniques on same
samples for independent corroboration of results
Electron
blocking
cell
Electronically
blocking
cell configuration
D
-10
IRion or IReon
-10.5
t
NMC523
NMC333
NCA
-11
0
Rion or Reon
R
Figure 3: Electronic conductivity as a function of Li content
for NEI 0and TODA
NCAs, TODA NMC333 and TODA NMC523
Z‘
IR
0
Z‘‘
U(t=)
0.2
NCA
Ag 0.8
0.6
Ionically
blocking cell configuration
Ion blocking
cell
x value in Li1-x(NMC-NCA)
At constant current, I
-4
D
Li+
Li PEO
e
e
e
e
Ag30oC
-2 0.4 At
D
IR
0
t
Li+
PEO Li
Li+
NCA
U(t=)
IRion or IReon
-6
Li+
Electronically blocking cell configuration
Z‘‘
D
U
Allows rate-limiting transport species and
paths to be understood up to high charge
voltage necessary to realize near-theoretical
capacities of layered oxide cathodes
Research Details
Li+
PEO Li
Li+
NCA
At constant current, I
log/(Scm-1)
Significance and Impact
oC
At
Li 25
PEO
Ag
Ionically blocking cell configuration
-9.5
U
First measurements of bulk electronic and
ionic transport across the entire state-ofcharge range relevant to energy storage in
NCA and NMCs, the most widely studied
classes of Li-ion cathodes
logD/(cm2s-1)
Scientific Achievement
NCA
Li+
Li+
e
e
e
e
Ag
Rion or Reon
R
0
Z‘ NMC333
After 1st cycle loss
in a Li-ion cell
NMC523
NCA-NEI
NCA-TODA
-8
0
0.2
0.4
0.6
x values in Li1-x(NMC-NCA)
Findings: Across the entire Li concentration range relevant to
energy storage, electronic conductivity is ~104 higher than ionic
conductivity. Ion transport decreases with increasing Li vacancy
concentration, until electrochemical shock creates rapid
transport paths through microcracking
1. R. Amin, D.B. Ravnsbaek, Y.-M. Chiang, J. Electrochem. Soc. 162(7),
A1163-A1169 (2015). doi: 10.1149/2.0171507jes
2. R. Amin and Y.-M. Chiang, J. Electrochem. Soc., 163(8) A1512-A1517
(2016). DOI: 10.1149/2.0131608jes
Work performed at MIT
0.8