Life extension of lithium-ion batteries using bidirectional pulse current: Focusing on frequency

Vehicle-to-grid (V2G) interaction, as a two-way energy interaction technology between vehicle power batteries and the power system, has an interaction frequency that significantly affects the battery life degradation law. Based on this, aiming at the idle storage scenario of electric vehicle batteries, this paper conducts the design of two-way energy interaction working conditions based on bidirectional pulse current (BPC) and durability experimental tests, and focuses on the influence of the BPC frequency on the battery life degradation law. Experimental results demonstrate that, compared to calendar storage, applying a BPC frequency of no less than 0.025 Hz effectively prolongs battery life without altering the state of charge. Under a BPC with 0.5C, the life extension effect on the battery is enhanced as the frequency increases, achieving up to a 19.1 % improvement in calendar life and a 179.7 % enhancement in equivalent full cycle life at 0.1 Hz. Through electrothermal characteristics analysis, it was discovered that increasing pulse frequency reduces impedance and terminal voltage while temperature does not change significantly, thereby lowering the rate of internal kinetic side reactions. Further incorporating incremental capacity analysis and voltage curve reconstruction to analyze the internal degradation mechanism, a notable decrease in the anode loss of lithium-ion inventory was evident. This paper attempts to reduce the battery degradation cost in the medium-to-high-frequency interaction demands of the power system by conducting research on battery life degradation under the action of different BPC frequencies, and provides guidance for the management of battery durability in the development process of the new V2G technology system.