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Sodium Borates: Expanding the Electrolyte Selection for Sodium-Ion Batteries.

Authors :: Ould DMC
Menkin S
Smith HE
Riesgo-Gonzalez V
Jónsson E
O'Keefe CA
Coowar F
Barker J
Bond AD
Grey CP
Wright DS
Source :: Angewandte Chemie (International ed. in English) [Angew Chem Int Ed Engl] 2022 Aug 08; Vol. 61 (32), pp. e202202133. Date of Electronic Publication: 2022 May 03.
Publication Year :: 2022
Abstract: Sodium-ion batteries (SIBs) are a promising grid-level storage technology due to the abundance and low cost of sodium. The development of new electrolytes for SIBs is imperative since it impacts battery life and capacity. Currently, sodium hexafluorophosphate (NaPF <subscript>6</subscript> ) is used as the benchmark salt, but is highly hygroscopic and generates toxic HF. This work describes the synthesis of a series of sodium borate salts, with electrochemical studies revealing that Na[B(hfip) <subscript>4</subscript> ]⋅DME (hfip=hexafluoroisopropyloxy, O <superscript>i</superscript> Pr <superscript>F</superscript> ) and Na[B(pp) <subscript>2</subscript> ] (pp=perfluorinated pinacolato, O <subscript>2</subscript> C <subscript>2</subscript> (CF <subscript>3</subscript> ) <subscript>4</subscript> ) have excellent electrochemical performance. The [B(pp) <subscript>2</subscript> ] <superscript>-</superscript> anion also exhibits a high tolerance to air and water. Both electrolytes give more stable electrode-electrolyte interfaces than conventionally used NaPF <subscript>6</subscript> , as demonstrated by impedance spectroscopy and cyclic voltammetry. Furthermore, they give greater cycling stability and comparable capacity to NaPF <subscript>6</subscript> for SIBs, as shown in commercial pouch cells.<br /> (© 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)