Charge and Discharge Reactions of a Lead Fluoride Electrode in a Liquid‐Based Electrolyte for Fluoride Shuttle Batteries:‐The Role of Triphenylborane as an Anion Acceptor‐

Abstract

Lead fluoride (PbF2) is a promising electrode material for fluoride shuttle batteries (FSBs) owing to its high theoretical capacity (219 mAh g–1). In this study, the discharge and charge capacities of a PbF2 electrode were measured using a bis[2‐(2‐methoxyethoxy)ethyl] ether containing cesium fluoride and triphenylborane as an electrolyte. A high specific capacity was maintained during both the discharge and charge processes in the first cycle, but the capacity decreased from the first charge process to the following discharge process. To clarify the electrochemical reaction mechanism, the dissolution and change in the electronic state of Pb at the PbF2 electrode during the discharge and charge processes were evaluated via atomic absorption spectrometry (AAS) and X‐ray photoelectron spectroscopy (XPS). The results obtained from AAS and XPS indicated that Pb was formed during the discharge process. Conversely, the formation of PbF2 and dissolution of Pb coexisted within the wide range of charge process. The PbF2 could react in the following cycle, but the dissolved Pb was unable to contribute to the following discharge/charge reaction. Therefore, after the initial charge process, the capacity decreased.

Initiating a Room‐Temperature Rechargeable Aqueous Fluoride‐Ion Battery with Long Lifespan through a Rational Buffering Phase Design

“…The specific capacity is comparable with previously reported FIBs with organic or solid electrolytes (Figure S15, Supporting Information). [ 1c,d,2a,3a,6a,7,8,30 ] A high energy density of 111.6 Wh Kg –1 is achieved based on the mass of BFO. The CE of BFO is much higher (93.1%) than that of BF (60.9%) and reaches nearly 100% at higher current densities.…”

“…a) CV curves of BFO and PB at 2 mV s –1 measured with a three‐electrode system; b) CV curves at various scan rates, c) linear relationship between I p and the square root of the scan rate, d) GCD profiles at 1 A g –1 , e) rate performance of BFO//PB battery, f) cycling stability comparisons with previously reported FIBs; [ 1d,2a,b,3a,6a,7,8,19a,30b–f,31 ] g) cycling stability of BFO//PB battery, and h) operating temperature comparisons with previously reported FIBs. [ 1a,d,2a,3a,8a,30e,f,31a,32 ] …”

“…Latterly, several ionic liquid and organic electrolytes were reported. [ 2b,6 ] But metal fluoride electrolyte salts are universally insoluble in organics at concentrations exceeding 0.05 m . [ 5a ] Anion acceptor (AA) or polymer ligands are needed to increase the solubility of F – .…”

“…[ 5a ] Anion acceptor (AA) or polymer ligands are needed to increase the solubility of F – . [ 6,7 ] Unfortunately, the use of AA would cause serious dissolution of active materials during cycling. [ 8 ] Another strategy to improve the solubility is to develop suitable organic fluoride electrolyte salts, such as N , N , N ‐trimethyl‐ N ‐neopentylammonium fluoride (Np 1 F) and N , N , N ‐dimethyl‐ N , N ‐dineopentylammonium fluoride (Np 2 F).…”

“…As to electrode materials, BiF 3 is a highly promising electrode material for FIBs due to its three‐electron reduction reaction and high theoretical specific capacity (≈302 mAh g –1 ). [ 6b,8a,11 ] The main problem of BiF 3 is its poor electronic conductivity that would result in inferior kinetics and poor energy efficiency. Another issue is volume expansion generally exists during the conversion reactions, which is caused by the large cell volume differences between BiF 3 and Bi.…”