Zwitterionic Materials for Enhanced Battery Electrolytes

Abstract

Zwitterions (ZIs), which are molecules bearing an equal number of positive and negative charges and typically possessing large dipole moments, can play an important role in improving the characteristics of a wide variety of novel battery electrolytes. Significant Coulombic interactions among ZI charged groups and any mobile ions present can lead to several beneficial phenomena within electrolytes, such as increased salt dissociation, the formation of ordered pathways for ion transport, and enhanced mechanical robustness. In some cases, ZI additives can also boost electrochemical stability at the electrolyte/electrode interface and enable longer battery cycling. Here, a brief summary of selected key historical and recent advances in the use of ZI materials to enrich the performance of three distinct classes of battery electrolytes is presented. These include: ionic liquid‐based, conventional solvent‐based, and solid matrix‐based (non‐ceramic) electrolytes. Exploring a greater chemical diversity of ZI types and electrolyte pairings will likely lead to more discoveries that can empower next‐generation battery designs in the years to come.

The role of zwitterionic crosslinks in facilitating ion conduction, lithium deposition, and stable interface formation for polymer electrolyte-based lithium metal batteries

“…18 The zwitterion in the polymer structure led to the decrease in t Li + , which might be due to the interaction between the zwitterion and Li + , which further led to an increase in resistance to Li + motion. 30,44…”

“…Their strong dipole moments generated by the zwitterionic molecular structure can promote the dissolution of lithium salt. 28–30 This type of molecule could also interact with anions as well to adjust ion distribution. 31 Zwitterionic molecules have also been covalently linked to polymer chains to prepare zwitterionic polymers.…”

Electrostatic Correlations Lead to High Capacitance in Zwitterion-Containing Thin Films

“…16,17,23−28 So far, zwitterions have primarily been investigated as additives to other electrolytes in batteries, but their application as a whole electrolyte is gradually increasing. 29,30 Zwitterions have also been used as highly polar dopants and functional coatings to affect the molecular orientation in liquid crystals to facilitate low driving voltage and large contrast smart windows for flexible wearable devices. 31,32 More broadly, zwitterions have been extensively studied for applications such as surfactants, surface coatings, and catalysts 33−37 and typically pose a significantly lower risk to aquatic species compared to their IL counterparts.…”

“…The usefulness of ILs in devices such as batteries and fuel cells is, however, limited by the competing migration rate of the component ions under an applied electric field. − The high ionic conductivity of ILs can also be detrimental in organic electrochemical transistors, often causing slower than desired switching speeds due to their intercalation into the semiconductor. − Zwitterions, in which the cationic and anionic functional groups are covalently bound, are molecules with zero net charge, making them promising alternatives to ILs. Their tethered structure allows the rotational reorientation of molecules under an applied electric field, avoiding its translational motion and allowing the mobility of only the target ions. ,,− So far, zwitterions have primarily been investigated as additives to other electrolytes in batteries, but their application as a whole electrolyte is gradually increasing. , Zwitterions have also been used as highly polar dopants and functional coatings to affect the molecular orientation in liquid crystals to facilitate low driving voltage and large contrast smart windows for flexible wearable devices. , More broadly, zwitterions have been extensively studied for applications such as surfactants, surface coatings, and catalysts − and typically pose a significantly lower risk to aquatic species compared to their IL counterparts …”