Coulombic efficiency of a sealed, thin plate, spiral lead-acid battery

Optima Advanced Technologies has developed prototype 15 Ah valve regulated, sealed, thin plate spiral lead-acid batteries for hybrid electric vehicle applications. These batteries were evaluated for coulombic efficiency using charge rates ranging from 1.5 A to 24 A. Pressure and temperature data were also collected, to investigate gassing behavior unique to valve regulated lead-acid batteries. Unlike conventional thick plate traction batteries, this battery had coulombic efficiencies as high as 98% for 100% charge replacement, making it desirable for hybrid applications. Both coulombic and energy efficiency decreased as the charge rate increased, as might be expected. The energy efficiency decrease was greater than the coulombic efficiency due to polarization effects. The characteristic voltage peak near the end of the charge was found to correlate closely with the pressure behavior. At low charge rates, the pressure stays below the cracking pressure of the valve, indicating that the peak in pressure observed is due to gassing and recombination, rather than venting