The Direct Forming of Ternary Metal Fluoride Thin Film Electrode By Pulsed Laser Deposition

Abstract

The rechargeable Li-ion batteries are the preferred the energy storage devices for electric vehicles and portable electronics. The potential probability of leakage and combustion caused by liquid electrolyte is being the current challenge. In recent years, the concept of all-solid-state thin film batteries has been mentioned due to the requirement of safety and flexibility. However, the conventional cathodes with low special capacity (140-170 mAh g-1) limit the improvement when used the next-generation anodes Sn and Si. Specifically, the fluoride-based materials have been the interests once again due to the higher theoretical capacities (3 to 4.2 times to the commercial cathodes).[1] More recently, a new insight into the mechanisms involved in ternary metal fluorides, which is designed the possibility of solid-solution Cu0.5Fe0.5F2 to figure out the poor electronic conductivity, large polarization and cyclic instability in the binary transition-metal fluoride.[2]In this work, we have been increasingly interested in the direct synthesis of the electro-active Cu0.5Fe0.5F2 thin films electrodes by Pulsed Laser Deposition approaches. Thin film depositions were performed from high purity LiF, Fe and Cu mixed targets (mol ratio 4:1:1) at room temperature. The initial electrochemical oxidation occurs at the first charge to form solid-solution Cu0.5Fe0.5F2 shown in the CV curve. During the delithiation process, the oxidation of Fe (Fe0 to Fe2+) occurs at 3.0 V, and further oxidation to higher valence state at 3.3 V. In the higher voltage region, the oxidation peak at 3.8 V indicated the conversion from Cu0 to Cu2+ and the forming of solid-solution Cu0.5Fe0.5F2. The lithiation process is quite different from the charge process. The CV curve clearly indicated the reduction of Fe and Cu presented overlap range from 3.7 V to 3.2 V, which may promoted the conversion to forma disordered rutile-like Cu–Fe–F phase. The final results may weaken the low hysteresis of Fe and the dissolution of Cu. The novel ternary metal fluoride is appealing for use in all-solid-state thin film Li-ion batteries.Fig.1 The cyclic voltammetry curve of Cu0.5Fe0.5F2 at scan rate 0.1 mV/s.Reference[1] Donato E. Conte, Nicola Pinna, A review on the application of iron(III) fluorides as positive electrodes for secondary cells, Mater Renew Sustain Energy (2014) 3:37.[2] Feng Wang, Sung-Wook Kim, Jason Graetz, et al. Ternary metal fluorides as high-energy cathodes with low cycling hysteresis, NATURE COMMUNICATIONS (2015) 6:6668. Figure 1