Abstract
Derating is widely applied to electronic components and products to ensure or extend their operational life for the targeted application. However, there are currently no derating guidelines for Li-ion batteries. This paper presents derating methodology and guidelines for Li-ion batteries using temperature, discharge C-rate, charge C-rate, charge cut-off current, charge cut-off voltage, and state of charge (SOC) stress factors to reduce the rate of capacity loss and extend battery calendar life and cycle life. Experimental battery degradation data from our testing and the literature have been reviewed to demonstrate the role of stress factors in battery degradation and derating for two widely used Li-ion batteries: graphite/LiCoO2 (LCO) and graphite/LiFePO4 (LFP). Derating factors have been computed based on the battery capacity loss to quantitatively evaluate the derating effects of the stress factors and identify the significant factors for battery derating.
Highlights
Li-ion batteries have the potential to shape global demand for fossil fuels, increase the use of renewables in the electric grid by buffering the intermittent and fluctuating green energy supply, bring convenient electric power to portable consumer electronics devices, and enable the broad commercial launch of electric vehicles
Where the derating factor can be used to reflect the rate of battery capacity loss according to Equation (3), the degradation rate refers to the rate of capacity loss
The derating factor declines against the decreasing state of charge (SOC), so the SOC can be derated to reduce the rate of capacity loss and prolong the battery calendar life
Summary
Li-ion batteries have the potential to shape global demand for fossil fuels, increase the use of renewables in the electric grid by buffering the intermittent and fluctuating green energy supply, bring convenient electric power to portable consumer electronics devices, and enable the broad commercial launch of electric vehicles These batteries, similar to any other engineering product, degrade and lose capacity with aging. Ecker et al [11] conducted an accelerated study on carbon/Li(NiMnCo)O2 cells to analyze the influence of cycle depth and mean state of charge (SOC) on cycle aging They observed that rate of aging increased with increasing cycle depth (∆SOC) almost linearly. Saxena et al [12] studied the effects of mean SOC and ∆SOC on graphite/LiCoO2 cells and concluded that both these factors affect the cycle life performance of batteries. The remainder of the paper is organized as follows: Section 2 defines the derating factor and discusses Li-ion battery derating for calendar life improvement; Section 3 discusses Li-ion battery derating for cycle life improvement; Section 4 presents conclusions
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