1,2,3-Trimethoxypropane: a bio-sourced glyme as electrolyte for lithium–O2 batteries

Abstract

Li–O₂ batteries are actively being investigated due to their high theoretical energy density (∼11 000 Wh kg⁻¹), which would compete with gasoline energy per Kg in electric vehicles. Linear glymes are the most appealing electrolytes for Li–O₂ batteries due to their large electrochemical window, stability against radicals and solubility of Li⁺ metal ions. However, all these superior properties are tarnished by their high toxicity. Herein, a greener glyme derived from bio-sourced glycerol (1,2,3-trimethoxypropane (TMP)), is proposed for the first time as a solvent in an electrolyte for Li–O₂ batteries. TMP performance has been compared to its toxic linear isomer, diglyme, and most popular tetraglyme as a liquid electrolyte and gel polymer electrolyte (GPE) membranes. GPEs were based on a mix of mono-, di- and tri- functional acrylates, cured simultaneously within a liquid electrolyte mix (1 M LiTFSI in the plasticizers) by UV-photopolymerisation. GPE-TMP based membranes showed a high ionic conductivity (2.33 × 10⁻³ S cm⁻¹ at 25 °C), directly comparable to the other glymes. Moreover, this remarkable conductivity was very close to the liquid TMP-based electrolyte (3.59 × 10⁻³ S cm⁻¹ at 25 °C). When used as electrolytes in lithium symmetrical cells, the GPE-TMP electrolyte enhanced the polarisation when compared to the liquid TMP-based cells, especially at higher rates (<0.6 V observed at ±1 mA cm⁻²). Performance in Li–O₂ cells showed that GPE-TMP electrolytes achieved a discharge capacity as high as 2.75 mA h cm⁻² (3819 mA h g⁻¹), ahead of GPE-diglyme or GPE-tetraglyme electrolytes (2.34 and 2.09 mA h cm⁻², respectively). When cycled, cells using TMP-based electrolyte had a similar capacity retention than the ones with tetraglyme, confirming the potential use of TMP as solvent/plasticizer in electrolytes for Li–O₂ cells.