Dendrite penetration in ceramic lithium conductors severely constrains the
development of solid-state batteries (SSBs) while its nanoscale origin remains
unelucidated. An in situ nanoscopic electrochemical characterization technique
is developed based on conductive-atomic force microscopy (c-AFM)
to reveal the local dendrite growth kinetics. Using Li7La3Zr2O12 (LLZO) as a
model system, significant local inhomogeneity is observed with a hundredfold
decrease in the dendrite triggering bias at grain boundaries compared
with that at grain interiors. The origin of the local weakening is assigned to
the nanoscale variation of elastic modulus and lithium flux detouring. An
ionic-conductive polymeric homogenizing layer is designed which achieves a
high critical current density of 1.8 mA cm–2 and a low interfacial resistance of
14 Ω cm2. Practical SSBs based on LiFePO4 cathodes can be stably cycled over
300 times. Beyond this, highly reversible electrochemical dendrite healing
in LLZO is discovered using the c-AFM electrode, based on which a model
memristor with a high on/off ratio of ≈105 is demonstrated for >200 cycles.
This work not only provides a novel tool to investigate and design interfaces
in SSBs but also offers opportunities for solid electrolytes beyond energy
applications.