modeling and analysis of lead-acid batteries with hybrid lead and carbon negative electrodes

Open Access
Author:
Gou, Jun
Graduate Program:
Mechanical Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
August 23, 2012
Committee Members:
  • Chao Yang Wang, Dissertation Advisor
  • Chao Yang Wang, Committee Chair
  • Michael Anthony Hickner, Committee Member
  • Christopher Rahn, Committee Member
  • Donghai Wang, Committee Member
Keywords:
  • modeling
  • lead-acid batteries
  • carbon electrodes
  • hybrid electrodes
  • gassing
  • current partitioning
Abstract:
Valve-regulated lead acid (VRLA) batteries used for hybrid electric vehicle (HEV) applications experience frequent high-rate partial state of charge (HRPSOC) cycling. The failure mode of VRLA batteries under HRPSOC cycling is accumulative sulfation in the negative electrodes. New HEV batteries, such as PbC batteries and UltraBatteries, based on the technologies combining conventional lead acid batteries and super capacitors have emerged in the last decade. PbC batteries replace the negative lead plate with an activated carbon (AC) plate, completely removing the sulfation in the negative electrode. UltraBatteries use a hybrid negative plate consisting of lead and AC materials and relieve the high-rate loads on the lead-acid cells and extend their lifetime. However, since the AC electrode material in PbC batteries and UltraBatteries lowers the battery energy density and increases gassing rate during charge, a model is useful to quickly optimize battery design and analyze gassing phenomena with different AC materials before physical prototypes. Further, the interactions between the battery and capacitor materials in an UltraBattery need in-depth understanding and the current partitioning between the two components needs to be predicted and evaluated. To date, both lead acid battery models and electrochemical capacitor models are available, but were developed separately. No models have been developed to understand the hybrid battery with presence of both battery and capacitive electrodes. In this work, a mathematical model for PbC batteries was firstly developed to predict performance under various operating conditions. This model couples the electrochemical, mass transport and thermal processes and also accounts for the gassing behaviors at electrodes during charge. With the feature of capacity and gassing rate predictions the model can serve as a design tool to compare and select desirable carbon candidates for specified applications of PbC batteries. The PbC battery model is applied to simulate and analyze the gassing and thermal behaviors during both galvanostatic charging and cycling processes. The galvanostatic charging processes with different gassing kinetics are investigated. Hydrogen gassing rate and charge efficiencies are focused on for cycling simulation and the effect of operational factors are demonstrated. The temperature rise due to gassing processes is compared among different electrode specifications. In addition, a fundamental model for UltraBatteries with lead-acid cells and capacitor cells was developed. Dynamic behaviors of internal parameters such as electrolyte potential and current density across the cells during cycling are revealed. One important parameter is introduced as a design ratio, namely the volume fraction of the lead electrode portion in the cell. The effect of design ratio on energy and power performance, such as capacity, current partitioning between cells and electrode utilization efficiency are studied through cycling simulations. Operational factors are evaluated as well, including the effects of duty ratio of a cycle, , starting SOC, cycling frequency and cycling current on current partitioning. This model unveiled the internal dynamics of current partition inside UltraBatteries through simulation results and offered guidelines for improving the design of batteries with hybrid electrodes and optimizing the operating strategies to reduce the peak discharge load on lead electrodes and thus prolong battery lifetime.