Poly(ionic liquid) iongels for all-solid rechargeable zinc/PEDOT batteries

Iongels composed of a polymer matrix and ionic liquids have been proposed as an alternative to liquid electrolytes for energy storage devices to prevent leakage and evaporation of the electrolyte which lead to device failure. Furthermore, the intrinsic nature of ionic liquid and poly(ionic liquid) promote the ionic conductivity in the iongels in comparison with solid polymer electrolytes, and prevent the exuding of the ionic liquid due to similarity in chemical structure. In this work, a series of poly(ionic liquid)-based iongels composed of poly(diallyldimethylammonium bis(trifluoromethanesulfonyl)imide), polyDADMATFSI, and 1-ethyl-3-methylimidazolium dicyanamide, [emim][dca], have been synthesised, and the effect of additives on the ionic conductivity are discussed. For example, the addition of Zn(dca)₂ salt in the iongel allows an increase of the ionic liquid content in the iongel, and therefore improves the conductivity due to the plasticiser effect of the ionic liquid. However, the maximum amount of IL in the iongel is limited by the self-standing properties of the solid material. Next, ceramic nanoparticles were added to the iongel which increased the ionic conductivity by promoting the cation-anion dissociation at the surface region of nanoparticles. Furthermore, the speciation and mobility of Zn²⁺in the iongel have been studied and compared with those in the neat [emim][dca], which interestingly follows a similar trend showing no impact of the poly(ionic liquid). Thus, the optimised iongel presented similar ionic conductivity (1.1 × 10⁻² S/cm) to that of the neat IL (4.1 × 10⁻² S/cm) and a larger electrochemical window (e.g. 4 V) that the neat IL (e.g. 2 V). Finally, all-solid rechargeable Zn/PEDOT battery has been assembled and cycled, proving its capability to perform as electrolyte in rechargeable Zn batteries.