CALCE Battery Group

    Battery performance and reliability is highly dependent on both the environmental and operational loads. When characterizing a battery for a specific application, the actual field conditions should be considered. These conditions include the range of current rates that will be used during charging and discharging, upper and lower voltage limits, charging and discharging profiles (pulsed current, constant current), battery pack configuration, length of standby time, temperature range, and mechanical loading. When conducting accelerated testing, loading should be applied so that only the failure mechanisms relevant to field usage are stressed.

    CALCE has investigated several different battery chemistries using various load profiles and environmental conditions. In the figure below, the top half shows the current and voltage profiles for a battery discharged with a pulsed current between 0A, 0.55A, and 1.1A each for 30 seconds. The bottom half shows a cycle life test in which the discharge cut-off voltage was changed after every cycle.
    (top) Pulsed current discharge profile for a lithium Ion battery. (bottom) Constant current discharge profile with varying discharge cut-off voltages.

    The figure below depicts the calculated capacities for each discharge cycle of a battery that was tested at 2 different constant current profiles at 2 different temperatures. It can be seen from Figure 4 that battery capacity (the amount of charge the battery can deliver) increases with increasing temperature and decreasing current rate. However, battery cycle life is reduced with increased temperature, so while temperature may have a positive effect on the single use performance of a battery, it has a negative effect on the overall lifetime reliability.

    Capacity vs Cycle data for a battery discharge using 2 different constant current loads and two different temperatures