Enabling Mg‐Based Ionic Liquid Electrolytes for Hybrid Dual‐Ion Capacitors
Paul Meister, Verena Küpers, Martin Kolek, Johannes Kasnatscheew, Sebastian Pohlmann, Martin Winter, Tobias Placke
Abstract
Abstract We report on the reversible (de)intercalation of TFSI − anions from a Mg‐based ionic liquid electrolyte, Mg(TFSI) 2 in Pyr 14 TFSI, in graphite activated carbon hybrid dual‐ion capacitor (DIC) cells. The role of different pseudo reference electrodes (PREs) including Ag‐wire and Li metal is discussed regarding the comparability of different battery cells. We show that an Ag‐wire PRE is not suitable for the designated purpose, while the use of a Li metal PRE results in high reproducibility. Mg‐based DIC cells are compared with cells based on pure Pyr 14 TFSI and LiTFSI‐Pyr 14 TFSI electrolytes, and with graphite Li metal dual‐ion cells employing LiTFSI‐Pyr 14 TFSI. At 5.2 V vs . Li|Li + , Mg‐containing DIC cells reveal an improved performance compared to Li‐based cells, i. e ., higher capacity (87 vs . 85 mAh g −1 ) and higher Coulombic efficiency (98 vs . 96 %). These results may pave the way to further studies and performance improvements of Mg‐based batteries and to hybrid DIC chemistries with other cations, especially multi‐valent ones.