Pulsed Charging Protocols with Non-Zero Relaxation Time for Lithium-Ion Batteries

Lithium-ion batteries are commonly charged following the constant current -constant voltage (CC-CV) protocol. Current flow during charging implies an equivalent ionic flow through the battery materials. Intercalation and de-intercalation of Li+ are accompanied by concentration gradients that are reflected by the rise in the cells' potentials that is required to maintain the constant current during the CC regime. In this work, two new pulsed charging protocols were tested. Firstly, a square current pulse is applied to the cell until the cut-off voltage is reached, followed by a pulsed square voltage protocol (PV). The second methodology keeps the same current pulse, however, after the limiting voltage was reached, the pulsing regime consisted in alternating between a maximum voltage value and a minimum, non-zero, constant current value. Different voltage pulse widths and frequencies were tested, in order to study the maximum electrodes' capacity, the time required to reach that capacity, the contribution of each individual step (i.e. PC and PV) to the total electrodes' capacity, and the thermal variations for each. The second pulsing mode produced capacity values 7%-8% higher than in the classical CC-CV protocol, and in charging times periods from 5%-25% faster, without compromising the batteries' cycle life.