Heteroleptic Coordination Polymer Electrolytes Initiated by Lewis-Acidic Eutectics for Solid Zinc–Metal Batteries

Solid polymer electrolytes (SPEs)
offer a viable path
for overcoming
the interfacial problems caused by side reactions and irregular deposition
in rechargeable Zn (zinc)–metal batteries. However, this potential
has been hampered by limited Zn2+ mobility in polymers;
a central conundrum remains on how to solvate Zn2+ strongly
enough to free it from anionic traps but weakly enough to minimize
its migration barriers. Inspired by biologically dynamic Zn functions,
we report a general strategy for constructing highly Zn2+-conductive SPEs by the engineering of heteroleptic coordination.
Leveraging polymerization catalyzed by Lewis-acidic Zn2+ predissociated eutectics, we stoichiometrically integrate polymeric
ligands (polyacrylamide) with kindred small-molecule co-ligands (acetamide)
for Zn2+ centers. This heteroleptic configuration allows
for the formation of entropy-increased ion channels with both labile
Zn2+–polymer bonding and accelerated polymer mobility,
warranting conductivity gains of 2 orders of magnitude and doubling
the Zn2+-transference number to 0.44, compared with traditional
SPEs. The applicability of the proposed heteroleptic coordination
design is also demonstrated by the improved reversibility of Zn plating/stripping
process (1200 h) and prolonged cycle life of solid Zn–metal
batteries (350 cycles with Mo6S8 cathodes) with
improved Coulombic efficiency (∼99%). This study underscores
the importance of tailoring the coordination environment in improving
cationic mobility in polymers.