  The most promising solid electrolytes for all-solid-state Li batteries are
oxide and sulfide ceramics. Current ceramic solid electrolytes are brittle and
lack the toughness to withstand the mechanical stresses of repeated charge and
discharge cycles. Solid electrolytes are susceptible to crack propagation due
to dendrite growth from Li metal anodes and to debonding processes at the
cathode/electrolyte interface due to cyclic variations in the cathode lattice
parameters. In this perspective, we argue that solutions to the mechanics
challenges of all-solid-state batteries can be borrowed from the aerospace
industry, which successfully overcame similar hurdles in the development of
thermal barrier coatings of superalloy turbine blades. Their solution was to
exploit ferroelastic and transformation toughening mechanisms to develop
ceramics that can withstand cyclic stresses due to large variations in
temperature. This perspective describes fundamental materials design principles
with which to search for solid electrolytes that are ferroelastically
toughened.
