Using siloxane-based liquid electrolytes with high stability for fluoride shuttle batteries

Abstract

To exploit the excellent safety as well as the thermal and electrochemical properties of siloxane-based liquid electrolytes, 2,2,4,4-tetramethyl-3,8,11,14,17-pentaoxa-2,4-disilaoctadecane was used as an electrolyte for the first time in a fluoride shuttle battery system.

Towards the high energy density batteries via fluoride ions shuttling in liquid electrolytes: A review

“…Since alkali metal compounds are shown to easily intercalate into carbon additive 45 of the positive electrode in the presence of G4, which causes loss of contact and further volume changes, the same setup of 1100 rpm ball‐milled BiF 3 /C 44 is tested within a siloxane‐based organic‐inorganic electrolyte [2,2,4,4‐tetramethyl‐3,8,11,14,17‐pentaoxa‐2,4‐disilaoctadecane (Sx)] instead of organic G4 solvent 46 . A wider stability window with the oxidation and reduction peaks was observed via cyclic voltammetry (above +0.6 V and below −2.8 V [ vs REF], respectively).…”

“…The electrochemical discharge and charge curves at (A) 25°C and (B) 55°C (reproduced from Reference [46] with permission from the Royal Society of Chemistry)…”

Evolution of fluoride shuttle battery reactions and three-dimensional morphology changes of BiF3 microparticles in an ethylene carbonate-based liquid electrolyte

“…Fluoride shuttle batteries (FSBs), in which fluoride or fluoride ions carry charges between an anode and a cathode, are considered as candidates for future batteries with high energy densities, and they have been extensively studied. 1–24 Defluorination of metal fluorides and fluorination of the resultant metals described below are often used as battery reactions.MF x + x e − → M + x F − (at the positive electrode, M being a metal)M′ + y F − → M′F y + y e − (at the negative electrode, M′ being a metal)Initial examples of rechargeable FSBs are all solid state types, in which a solid electrolyte was used at an elevated temperature of 150 °C to increase ionic conductivity. 3,4 Then the use of several liquid electrolytes for FSBs at room temperature was demonstrated, showing charging 5 and charge–discharge cycles of FSBs 6 and defluorination–fluorination cycles of single electrodes.…”

“…3,4 Then the use of several liquid electrolytes for FSBs at room temperature was demonstrated, showing charging 5 and charge–discharge cycles of FSBs 6 and defluorination–fluorination cycles of single electrodes. 10,11,15 As solvents in these electrolytes, an ionic liquid, 6 glymes, 8–11,16–19 siloxane, 20 γ-butyrolactone 21 and partially fluorinated ether 15 were used. It is difficult to dissolve fluoride sources in many organic solvents.…”

“…Thus, LiBOB 17 or LiPF 6 8,16,19 was dissolved in glymes to enhance the solubility of CsF (a fluoride source). Anion acceptors were also added to glymes 9–11 and siloxane 20 to dissolve CsF. It is also difficult to develop electrolytes with wide potential windows for using active materials, such as AlF 3 and CeF 3 , with low oxidation/reduction potential close to Li + /Li (AlF 3 : about 0.8 V vs .…”