Fast Charging Protocols based on Pulse-Modulation with Varying Relaxation for Electric Vehicle Li-ion cells

Abstract

Fast charging lithium-ion batteries (LIBs) remain as a key factor to enhance in battery powered systems such as electric vehicles (EVs), grid battery energy storage systems (BESS) or portable electronics. Because of the inherent multidisciplinary engineering impacts of the LIB charging process, the design of an optimal fast charging method is challenging. Fast charging is mostly compromised by the deterioration of the health of the battery in terms of both capacity and power fading, and safety. Hence, it is essential to design better fast charging protocols to improve the acceptability, reliability and marketability of battery powered systems. In addition, emerging LIB technologies containing blended silicon-graphite (Si-Gr) with improved energy densities are expected to become widely used in next-generation systems. Hence the design of novel, technology-oriented charging schemes are required. This paper examines the suitability of different pulse charging patterns for fast charging, coupled with varying relaxation schemes applied on commercial, high-energy density Si.Gr cells. The Pulse relaxation is expected to reduce the overpotential stress driven by high-rate currents and constant current charging. By measuring the Internal Resistances (IR) distribution over the state of charge (SOC), a favorable SOC range for high C-rate charging is obtained. As a practical reference point, the fast charging schemes targeted the charging time from the manufacturer's standard 4 h-charge scheme to 1 h, while maintaining safe cell temperature and voltage. A table of comparison provides charging and power efficiencies, temperature rise and charge percentage as a summary of a set of interesting fast charging schemes. The presented results provide a set of insights and indicators to better understand and improve pulse charging design schemes on this specific Si-Gr based battery.