A review of float charging in lithium-ion batteries: Degradation mechanisms, influencing factors, and optimization strategies

Lithium-ion batteries (LIBs) are increasingly being used in backup energy storage applications such as on-grid substations and solar systems, where maintaining a full state of charge is essential to ensure immediate availability and delivery of rated capacity. As a result, float charging, which involves supplying a low, continuous current to maintain the battery's charged potential and counteract self-discharge, is used to ensure batteries remain fully charged. However, prolonged float charging can lead to battery degradation caused by electrolyte decomposition, deposition of metallic lithium, and structural changes of the electrodes, compromising battery lifespan, performance, and safety. This review discusses the factors that influence float charging behavior, including the selection of float voltage, and ambient temperature. It also examines the associated degradation mechanisms and strategies to optimize float charging conditions for improved performance and longevity in stationary energy storage applications.