Potential dependent formation of fluorine-rich artificial interfaces for durable dual-ion batteries

Abstract

The mechanochemically fragile cathode-electrolyte interphase (CEI) cannot protect the anion-storing carbon cathodes against high voltage (>4.5 V) corrosion. The strategy of preforming a fluorine-rich artificial interface is opted here. Two potentially dependent interfaces are derived using Fluoroethylene carbonate (FEC) as an electrolyte additive at high voltage (2.0–5.0 V) and low voltage (0.35–2.00 V). Both high voltage interface (HVI) and low voltage interface (LVI) assist in retaining >87 % capacity over 200 cycles, while the unmodified pristine electrode loses >13 % capacity within 50 cycles only. The interfacial stability enhances more in HVI, which cycles 500 times with 90 % capacity retention, whereas LVI loses >13 % capacity within 200 cycles. The reason is attributed to the fact that the potential-dependent decomposition of FEC follows two separate mechanistic routes, thereby resulting in two chemically dissimilar interfaces (HVI and LVI) that behave differently under the circumstances of PF6− storage. The LVI undergoes dynamic evolution with cycling. The results are impermeably thick CEI, ruptured bulk with a loss in graphitic order, and a weaker electrochemical output. In contrary, the HVI-protected surface subdues electrolyte decomposition to the greatest extent and yields the most durable dual-ion battery.