Series-connected multi-cell operation of lithium-ion cells by floating method

The resistance to damage during overcharge and overdischarge of a single cell and the possibility of series-connected multi-cell operation have been investigated using a commercialized lithium-ion cell. The single cell showed sufficient cycleability in overcharge up to 4.5 V and small reversible capacity in overdischarge under 2.5 V. An overdischarged cell below 0 V did not generate subsequent electromotive force and behaved like a resistor of an electron conductor. Multi-cell operations including imbalanced cells both in a preshifted state-of-charge between +30 and −5% and in various ambient temperatures were performed for over 1000 cycles of charge/discharge by the floating method.