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What is Voltage Delay

Published time: 2017-1-15 8:18:24, Publisher: Green Energy Battery Co., Ltd

When a battery is taken from the shelf and put on load for the first time, the cell voltage will drop from open circuit voltage (OCV) to an operating voltage that is a function of the discharge current. At low currents, the voltage level will stabilize instantly. However, at higher current values, there may be a transition period, during which the initial voltage drops below the plateau voltage before recovering. During this period, voltage may stay above the application cut-off voltage which is typically between 2.5 V and 3.0 V. If current increases even more, voltage may drop below cut-off for a short time. The time before it recovers to the application cutoff is referred to as the delay time and the lowest value of voltage reached is called the transient minimum voltage (TMV). The voltage delay phenomenon is due to passivation. It is related to the protective layer that forms on the anode surface. Once a battery has been depassivated which means voltage has reached the normal plateau of operation it will not passivate again unless there is a subsequent long period on open circuit.

The degree of passivation is a function of storage time, current, temperature during storage, and mechanical aspects. Thus, passivation will usually grow with storage time and temperature. Depassivation can be effected by current flow as well as mechanical shocks, vibration, and temperature cycling. As a rule of thumb a current of 2 μA/cm2 of lithium anode surface area will prevent passivation and allow for immediate voltage response above typical application cut-off values. The same can be achieved by daily pulses corresponding to equivalent or slightly smaller average values.