Electrochemically driven conversion reaction in fluoride electrodes for energy storage devices

Abstract

Exploring electrochemically driven conversion reactions for the development of novel energy storage materials is an important topic as they can deliver higher energy densities than current Li-ion battery electrodes. Conversion-type fluorides promise particularly high energy densities by involving the light and small fluoride anion, and bond breaking can occur at relatively low Li activity (i.e., high cell voltage). Cells based on such electrodes may become competitors to other envisaged alternatives such as Lisulfur or Li-air systems with their many unsolved thermodynamic and kinetic problems. Relevant conversion reactions are typically multiphase redox reactions characterized by nucleation and growth processes along with pronounced interfacial and mass transport phenomena. Hence significant overpotentials and nonequilibrium reaction pathways are involved. In this review, we summarize recent findings in terms of phase evolution phenomena and mechanistic features of (oxy)fluorides at different redox stages during the conversion process, enabled by advanced characterization technologies and simulation methods. It can be concluded that well-designed nanostructured architectures are helpful in mitigating kinetic problems such as the usually pronounced voltage hysteresis. In this context, doping and open-framework strategies are useful. By these tools, simple materials that are unable to allow for substantial Li nonstoichiometry (e.g., by Li-insertable channels) may be turned into electroactive materials.

Liquid Polydimethylsiloxane Grafting to Enable Dendrite‐Free Li Plating for Highly Reversible Li‐Metal Batteries

“…Lithium‐metal has the potential to become the next‐generation anode material due to its high theoretical specific capacity (3860 mAh g −1 ) and low redox electrochemical potential (−3.04 V vs standard hydrogen electrode) . When matched with conversion‐type S, sulfides, and fluorides, much higher energy densities (≈900 Wh kg −1 ) can be obtained for the corresponding Li‐metal batteries (LMBs) . However, the development of LMBs has been limited because of the poor cycling performance and safety issue caused by uncontrolled lithium dendrite growth .…”

Enhancement of dielectric and electric-field-induced polarization of bismuth fluoride nanoparticles within the layered structure of carbon nitride

“…Because of these properties, inorganic and organic fluorine compounds and fluoropolymers are employed for lithium batteries, fuel cells and capacitor applications 5 . Conversion-type fluorides have potential to achieve high energy density by involving the light and small fluoride anion 6 .…”

3D Starfish‐Like FeOF on Graphene Sheets: Engineered Synthesis and Lithium Storage Performance

“…Upon charging, a major oxidation peak at about 2.5 V, with a very small shoulder at about 3.15 V, is observed, which may be ascribed to the conversion and intercalation reactions, respectively. A clear positive shift in the cathodic (lithiation) peaks (2.4→2.8 V and 1.2→2.0 V) in subsequent cycles can be observed, as a consequence of morphology and compositional changes after the first cycle; this is commonly observed behavior for iron oxyfluoride based cathodes . From the second cycle onwards, the CV profiles remain steady and overlap well, which indicates the excellent reversibility of the FeOF/rGO electrode.…”