Battery capacity measuring method and apparatus

Abstract

A method for measuring the capacity of an electrochemical cell involving the sequential stepping of the voltage applied to the cell and measurement of the accumulated charge. On each voltage step the time dependence of the current passing through the cell is monitored and a step to a new voltage level is made when the current reaches a small but finite value I.sub.minimum, indicating a given level of charges has been attained. The values of the voltage and charge measured at the current level I.sub.minimum may be arbitrarily close to the thermodynamically determined values. Additionally, the time dependent current may be measured while the cell voltage is maintained constant to obtain the kinetic behavior of the battery. Thermodynamically and kinetically related parameters are useful for the performance characterization of electrochemical cells. Devices for implementing the instant method are disclosed where the electrochemical cell is automatically discharged and/or charged while measuring the cell voltage, instantaneous current, accumulated charge and time. The charging and discharging operations are controlled by digital logic circuitry or by a digital computer.