Lithium-Ion Battery Electrolyte Design for Extreme Fast-Charging
Authors: Guo Ning , McCloskey Bryan D. 
Published: December 2024

As the transition to electric vehicles accelerates, the need for fast charging of lithium-ion batteries (LIB) becomes increasingly important to address key consumer concerns such as range anxiety and limited charging infrastructure. Fast charging not only boosts the effective service capacity of charging infrastructure but also allows the use of higher-capacity batteries without long downtime. To advance the transition to EVs, the Department of Energy (DOE) has set high goals for extreme fast charging (XFC), where batteries should be charged to 80% capacity in under 10 mins[1].
Operating under XFC conditions gives rise to high overpotentials in LIBs. The graphite electrode potential can be driven to below 0 V vs Li/Li+ due to the fast-charging overpotential, making Li plating thermodynamically favorable. Metallic lithium can grow as dendrites that pierce the separator and short the battery, creating safety concerns.[2] Some metallic lithium can also become electronically isolated, referred to as “dead lithium”, that cannot be recovered upon discharge.[3] Consequently, lithium plating remains a critical problem during fast charging that decreases total Li inventory and degrades the battery's overall capacity. In addition, charging under XFC conditions usually results in poor charge acceptance due to a combination of overpotential and extreme concentration gradients in the electrolyte.[4], [5], [6] Poor charge acceptance limits effective XFC protocol charging time and prolongs the overall time needed to charge LIBs.
Our research investigates two concurrent strategies to enhance fast charging performance from fundamental considerations related to the electrolyte. In the first, a low-viscosity co-solvent such as acetonitrile is used to demonstrate the effect of improved electrolyte transport properties on fast charging. In the second, we show that the interfacial chemistry of graphite electrodes also plays a crucial role in fast charging. By developing a better understanding of the voltage-dependent formation mechanisms of the solid-electrolyte interface (SEI) with electrolyte additives such as FEC, we hope to leverage those insights into designing a better interface for XFC applications.
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