Empirical Sulfation Model for VRLA Batteries under cycling operation

Transcription

1 Empirical Sulfation Model for VRLA Batteries under cycling operation Marcel Franke, Julia Kowal Electrical Energy Storage Technologies Department of Energy and Automation Technology, TU Berlin Einsteinufer 11, Berlin, Germany 10 th International Conference on Lead-Acid Batteries June 2017, Golden Sands, Bulgaria

2 Motivation Ageing cycle test matrix SOH determination for stationary VRLA batteries OPzV batteries cycled under varying DODs for 4 weeks followed by capacity test Constant voltage limits Internal resistance R i determined 1s after charge/discharge switch Page 2

3 Motivation Internal resistance during cycling Charge acceptance (charged Ah per cycle) After capacity test (standard EN-charge) R i was restored to initial value! Page 3

4 Results lead to following questions: 1. Which impact factors during battery operation influence short term resistance growth and charge acceptance? 2. How do they influence short term resistance growth and charge acceptance? 3. How can such a behavior be modelled? Page 4

5 Internal resistance determination RR ii = ΔUU ΔII Instant of time after switch is deciding factor the shorter the better ΔU 1 : Higher ΔU better SNR but more effected by side reactions ΔU 2 : Smaller ΔU worse SNR but less effected by side reactions Page 5

6 Cycle matrix of selected tests Reference cell Cell U + [V] U - [V] I + [ma] I - [ma] T [ C] t CV [h] Test Setup 2.5 Ah small cylindrical cells with AGM separator All cells stored in climate chamber and cycled with Arbin BT2000 Test designed to have same Ah-throughput of 15 equivalent full cycles Capacity test performed before cycling, C 5 = 2.6 Ah Page 6

7 Effect of discharge current U + = 2.45 V, U - = 1.94 V, T = 25 C, t CV = 0 h, I + = 480 ma Page 7

8 Effect of CV-Time U + = 2.45 V, U - = 1.94 V, T = 25 C, I +- = 480 ma Page 8

9 Effect of end of charge voltage U - = 1.94 V, T = 25 C, t CV = 0 h, I +- = 480 ma Page 9

10 Effect of temperature and end of discharge voltage U + = 2.45 V, U - = 1.94 V, t CV = 0 h, I +- = 480 ma U + = 2.45 V, T = 25 C, t CV = 0 h, I +- = 480 ma Page 10

11 Summary of the effects Impact factor Discharge current I + low high Charge current I - low high End of charge voltage U + low End of discharge voltage U - low CV-Time short Temperature low high high long high Capacity test after cycling with extended charge (3 days at 2.3 V) C 5 from 1.35 Ah to 1.8 Ah R i could not be restored to initial value! Different behaviour than OPzV batteries Page 11

12 Modelling of the effects Model function RR ii xx = 1 + aa(tt CCCC ) xx bb II,UU aa tt CCCC bb II = 0.12 ee 0.54 tt CCCC = 0.93 ee 1.03 II bb UU = 1.95 UU RR ii xx = 1 + aa xx bb, 0 < b < 1 Effect of temperature and U + could not be evaluated properly xx = II tt [AAA] Page 12

13 Validation 1 I ma 720 ma 360 ma U V 2.45 V 2.45 V U V 1.94 V 1.96 V Previous history of battery: 480 ma, V, 1 h CV Page 13

14 Validation 2 I ma 480 ma 720 ma U V 2.30 V 2.30 V U V 1.96 V 1.94 V No History except capacity test and resting till validation Page 14

15 Conclusion Internal resistance gradient can be linked to charge acceptance Most influential factors are discharge current, CV-phase and DOD Behaviour can be described using root function Degeneration induced by CV-time and higher current is not considered in the model Future Work Further investigation of the different impact factors (T, U + ) Consideration of degeneration Develop robust method for determining R i Spongy lead electrode Page 15

16 Thank you very much! Page 16

17 Backup Page 17