Increased reliance on portable devices has resulted in a surging market for lithium ion batteries. A drawback of current lithium battery technology is the use of flammable organic electrolytes in these devices, which can lead to fire or explosion upon device failure. To mitigate these risks, solid electrolytes are being explored by numerous groups. While ceramic electrolytes offer the highest conductivity of known solid electrolytes, they are brittle, unstable to high-voltage electrodes, and can be resistive at grain boundaries. Organic electrolytes offer ideal physical properties making these materials amenable to device fabrication, but suffer from low conductivities, precluding their use in batteries. In this lecture, our new approach to generation of solid electrolytes is presented, which involves growth of organic-salt co-crystals. We target solid state structures where the “hard” (charge-dense, non-polarizable) lithium or sodium cations interact poorly with the “soft” (charge diffuse, polarizable) Lewis donor of the matrix molecule. Fortuitously, this class of electrolytes has an inherent nanoliquid surface region that facilitates grain binding to form a contiguous ionically conductive pellet, and imparting novel properties such as melt-press castability, self-healing, and a novel reversible “solvate-sponge” property, whereby application and relief of pressure can be used to respectively “juice” and re-absorb liquid solvent from the crystal structure.

Soft salt-organic solvate cocrystals as a new class of solid electrolyte for lithium and sodium batteries

ACS Spring 2022

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