Unifying electrolyte formulation and electrode nanoconfinement design to enable new ion–solvent cointercalation chemistries

Abstract

Electrochemical ion intercalation is a multi-step process typically involving transport of solvated ions through the liquid electrolyte phase, desolvation of ions at the electrochemical liquid/solid interface, and solid-state diffusion of bare ions within the host electrode. Instead of stripping solvent molecules at the interface during the desolvation step, ions can also intercalate together with a (partially) intact solvation sheath into the host electrode, giving rise to cointercalation chemistries. The thermodynamics and kinetics of ion–solvent cointercalation processes are fundamentally different from the more common case of bare ion intercalation. They offer the possibilities of improved kinetics, modified redox potentials, and enabling intercalation chemistries that are thermodynamically inhibited for bare ions. Thus achieving, identifying, and controlling electrochemical ion–solvent cointercalation are of importance to the field of electrochemical energy storage, particularly, in order to enable post-lithium cell chemistries. Herein, we analyze current efforts of electrolyte formulation and electrode nanoconfinement design to control (achieve or inhibit) cointercalation. Analytical tools to unambiguously identify cointercalation phenomena are discussed. While most current efforts singularly focus on the electrolyte formulation, we propose a unified approach of matching electrolytes with the host's nanoconfinement environment to broaden the range and increase the effectiveness of ion–solvent cointercalation chemistries for use in multivalent ion intercalation, low-temperature batteries, supercapacitors, or dual-ion batteries.