Kinetic analysis and alloy designs for metal/metal fluorides toward high rate capability for all-solid-state fluoride-ion batteries

Abstract

New concepts for electrochemical energy storage devices are required to handle the physicochemical energy density limit that Li-ion batteries are approaching. All-solid-state fluoride-ion batteries (FIBs), in which monovalent fluoride anions...

Reversible and Fast (De)fluorination of High‐Capacity Cu2O Cathode: One Step Toward Practically Applicable All‐Solid‐State Fluoride‐Ion Battery

“…In some cases of employing Pb/PbF 2 as anode, the discharging cut-off voltage can be even minus, which was also called "forced discharge" by Clemens et al [11] In terms of practical applications, La/LaF 3 anodes with lower potentials (−2.41 V versus Pb/PbF 2 ) have be used in many previous studies. [6][7]9,19] A preliminary assessment of Cu 2 O||LaF 3 cell compared with typical LiCoO 2 ||graphite was given in Table S1 (Supporting Information), where higher energy density can be achieved in Cu 2 O||LaF 3 cell; particularly, the volumetric energy density of Cu 2 O||LaF 3 , which is more meaningful for practical application, is almost twice that of LiCoO 2 ||graphite. If more ideal anode (such as Li/LiF which possesses the lowest electrode potential among various M/ MF x compound) can be practically employed as anode, the cell voltage can be further increased, as we have marked in the right-side axis of Figure 2a.…”

“…[1] In particular, the commercialization of lithium-ion batteries (LIBs) has contributed greatly to the establishment of an intelligent (de)fluorination, which have been proven in previous studies to be devastating for the electrode-electrolyte interfaces of allsolid-state batteries. [5][6][7]10] In addition to M/MF x systems, topotactic host materials with accessible lattices, such as perovskite-, Ruddlesden-Popper-, and schafarzikite-type materials, have also attracted widespread attention owing to their high structural reversibility and F intercalation tolerance. [11][12][13][14] However, these intercalation-type materials usually have heavy molecules, and the large mass ratios of the electrochemically inactive components lower the overall energy densities.…”

“…Meanwhile, the Cu 2 O cathode also possesses highly accessible non-close-packed Cu-O configurations; as expected, it was found to exhibit a muchimproved rate capability compared to that of a Cu/CuF 2 -based cathode. [6] X-ray absorption spectroscopic (XAS) results revealed a typical phase-transition reaction mechanism and investigated the structural evolutions, as well as the possible causes of the initial capacity fading. Kinetic factors that affect (de)fluorination were also discussed based on Kolmogorov-Johnson-Mehl-Avrami (KJMA) theory.…”

“…Thus far, the extraordinary performance of Cu 2 O (particularly the high performance at a current density of 375 mA g −1 ) using a bulk-type all-solid-state cell (Figure 1a) seems to be the best result among all related studies. [3,[5][6][7][8][9][10][11][12][13][14] The mixed-anion nature of fluorinated Cu 2 O also lead to some new considerations. It is hoped that this result will deepen our understanding on the development of new capable alternatives for all-solid-state FIBs, as well as bring new considerations toward the possibilities of practical applications of all-solid-state FIBs, considering the low-cost, highly commercialized, and chemical stable characteristics of Cu 2 O materials.…”

“…In early studies, including our recent ones, simple metal/metal fluoride (M/MF x ) systems were first used as electrode materials with high theoretical capacities. [3,[5][6][7][8][9] Using M/MF x systems, it is theoretically feasible to fabricate batteries with high energy densities because the working potential can exceed 3 V if suitable cathode-anode combinations are selected. However, closepacked metal atoms (e.g., Cu, Co, Ni, and Bi) provide no diffusion path for F anions in conversion-type M/MF x systems; as a result, M/MF x systems inevitably suffer from thorough atomic rearrangements and undesired volumetric changes upon All-solid-state fluoride-ion batteries (FIBs) are regarded as promising energy storage devices; however, currently proposed cathodes fail to meet the requirements for practical applications in terms of high energy density and high rate capability.…”