Abstract #995, 224th ECS Meeting, © 2013 The Electrochemical Society
Understanding the influence of conductive carbon
By comparing the discharge capacity, especially at
additives surface area on the rate performance of
higher rates, it can be concluded that the conductivity
LiFePO4 cathodes for lithium ion batteries
and electrochemical performance of LiFePO4 cathode is
a
b
a
Xin Qi , Berislav Blizanac , Jie Li , Martin Winter
a
a MEET Battery Research Center, Institute of Physical
significantly affected by the surface area, particle size
and morphology of the used carbon additives.
Chemistry, University of Muenster
Corrensstraße 46, 48149 Muenster, Germany
b Cabot Corporation
Mercury porosimetry was carried out to define the
porosity and pore size distribution of electrodes.
5401 Venice Avenue NE, Albuquerque, USA
600
Electrodes with
Porosity (%)
CB1
CB2
CB3
CB4
CB5
30.47
29.87
29.36
24.39
25.43
500
Performance of the cathode active materials in lithium
electronic conductivity, particularly the case for lithium
dV/dlog(D)
400
ion batteries is strongly influenced by their poor
300
iron phosphate (LiFePO4, LFP), which conductivity
200
below 10-9 S cm-1 [1, 2]. Conductive carbon additives
100
with different surface area and particle size, alone or in
0
0
10
20
30
40
50
60
70
80
Pore size (nm)
different combinations, were tested as conductive
additives for LiFePO4 cathode materials in lithium ion
Fig. 3: Porosity and pore size distribution of LFP electrodes with
batteries. Their influence on the conductivity, rate
5 different carbon blacks.
capability as well as the structure of the resulting
electrodes was investigated.
Carbon additives with higher surface area (smaller
3
particle size) create more contact points between the
active material particles and thus have a potential to
form a better conductive network in the electrode.
-1
Conductivity (S m )
CB3
2
However, if the particle size is too small it becomes
CB2
CB1
CB5
1
CB4
more difficult to properly incorporate conductive
additive into the electrode structure in addition to
challenges with dispersion and agglomeration. This
0
0
100
200
300
400
500
2
600
-1
Specific surface area (m g )
deteriorates the conductive network and increases
electrode resistivity. The electrode porosity is strongly
Fig. 1: Conductivity of LFP electrodes with the different carbon
affected by the dimensions of the carbon black: small
blacks.
carbon black in electrode leads to smaller pores and
lower porosity, thus is negatively affecting the
160
electrolyte accessibility. The results indicate that an
140
optimum electrode structure and thus performance can
-1
Capacity (mAh g )
120
100
be obtained by selecting a suitable combination of
80
carbon additive and active material.
60
40
20
0
0.1
CB1
CB2
CB3
CB4
CB5
References:
1
10
-1
Discharge Rate/ C-Rate (h )
Fig. 2: Discharge capacity as a function of discharge rate for
electrodes utilizing different conductive carbon additives.
[1] S. Y. Chung et al. Nature Materials 2 (2002) 123.
[2] A. K. Padhi et al. J. Electrochemical Society 144
(1997) 1188.