Electrochemical State Models of Lead-Acid Batteries.
MASSACHUSETTS INST OF TECH CAMBRIDGE
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In order to establish a model which would more accurately predict discharge characteristics of a cell at any arbitrary current, and which would better fit the family of discharge curves, testing was done based on the Shepherd equation using a transparent lead-acid battery. A set of dicharge curves at .6, 1.5, 3.6, and 5.4A, preceded by a 3.6A preconditioning discharge to remove the memory effect, was obtained. The battery was cycled continuously through deep discharges in an attempt to determine secular changes during the life of the battery. Several modifications to the Shepherd equation were proposed in order to obtain a better fit to discharge data. These included modeling the capacity as a function of current as QCI 1-n, Peukerts equation modeling the ohmic polarization as a linear function of accumulated charge and modeling the diffusion polarization as a function of accumulated charge alone and not current. Conclusions were drawn on the suitability of Shepherds equation. The inclusion of the changed ohmic polarization term gave a good fit for individual curves which also suggested the change in the diffusion polarization term. Since a small current density approximation was used in Shepherds equation, developing a model based on the original terms was recommended. Also recommended were the modification of a model to predict characteristics during a cycle with various discharge currents and further life cycle testing to determine the secular changes in the battery. Author
- Physical Chemistry
- Electrochemical Energy Storage