Methods for Estimating Available Capacity and Voltage Change of Stationary Lithium-ion Secondary Battery Under Operation

Abstract

Methods for estimating available capacity and voltage changes during the discharge of a large-capacity lithium-ion battery were developed and their effectiveness was demonstrated. The cell was developed for such uses as a backup in power supply systems etc. Lithium-ion cells with storage capacity ratings of 10 and 40Ah were exposed to high-temperature acceleration tests. We observed a correlation between a cell's available capacity and voltage drops that we believe is effective for estimating the available capacity of the cell. We were able to predict the voltage change in a varying load-current discharge with a high degree of accuracy. This is because for a lithium-ion cell, the voltage change profile in a stepwise-varying constant-current load can be expressed as a conjunction of partial discharge voltage curves of first, second and other sequent discharge current every time discharge duration of each constant current is terminated. We believe the methods are practical as a monitoring function in power systems equipped with a lithium-ion battery.