Page 238 - Handbook of Battery Materials

7.3 Physical Properties of the Bromine Storage Phase 207

Table 7.7 Conductivity λ of the polybromide phase
2+
at 50% SOC and various contents of Zn .
–1
◦
−1
[Zn ](mol L ) λ (S cm ) Temperature ( C)
2+
0.00 3.42 × 10 −2 20
0.07 3.53 × 10 −2 20
0.60 2.76 × 10 −2 20
0.95 2.07 × 10 −2 20
2.05 0.58 × 10 −2 21

Taken from Ref. [70].

MEM MEP
100
60 40°C 40°C
80
50 30°C 30°C
spec. rest. / mS cm 40 20°C 60 20°C
10°C
30
40
10°C
20
0°C
10
−10°C 20 0°C
−10°C
0 0
1 2 3 1 2 3
mol Br 2 / mol complexing agent
Figure 7.5 Isotherms for the conductivity of pure MEM and
−1
MEP-complex phases (mS cm ) versus degree of added
Br 2 . Taken from Ref. [63].
energy for the transport of charge can be obtained applying Arrhenius’ equation,
E A
−
k = k 0 e RT (7.1)
Niepraschk [63] found 23.4 kJ mol −1 for pure MEMBr complex and 16.5 kJ mol −1
for pure MEPBr complexes at 3 mol Br 2 /mol complexing agent. These values
increase slightly with decreasing concentration of Br 2 . A value of E A of 11.5 kJ
mol −1 for a complex phase containing MEP:MEM in the ratio 3 : 1 at comparable
contents of Br 2 was reported by Hauser [70].
7.3.2
Viscosity and Specific Weight

The kinematic viscosity of MEM containing aqueous electrolytes at different
concentrations of MEM and ZnBr 2 and at different temperatures has been studied
66 (see Table 7.8).