Ideal benefits of exceeding fixed voltage limits on lithium-ion batteries with increasing cycle age

Abstract

This work quantifies what can safely be gained in terms of charged energy by disregarding conventional fixed limits on lithium-ion cell terminal voltage and instead placing limits on side reaction overpotential. A high-fidelity lithium-ion battery cell model is subjected to a range of constant currents given a set of initial states of charge (SoC). With limits placed on side reaction overpotential, it is possible to safely charge additional energy into the cell after the voltage limit has been reached. The effects of cell ageing through solid electrolyte interphase build-up are included in the model and both a fresh cell and a 4000 cycles aged cell are thereby investigated. It is shown that limiting anode plating overpotential instead of terminal voltage results in a theoretical additional 6% of total cell energy capacity charged for a fresh cell and 4% for an aged cell. Furthermore, with low enough initial SoC a 10C current is safe for five to ten seconds after exceeding the cell voltage limit depending on cell age. When evaluated on a city bus drive cycle, use of plating overpotential limits over voltage limits is shown to enable additional recovery of 2.5–14% of traction energy.