  The control of the dielectric and conductive properties of device-level
systems is important for increasing the efficiency of energy- and
information-related technologies. In some cases, such as neuromorphic
computing, it is desirable to increase the conductivity of an initially
insulating medium by several orders of magnitude, resulting in effective
dielectric breakdown. Here, we show that by tuning the value of the applied
electric field in systems { with variable permittivity and electric
conductivity}, e.g. ion intercalation materials, we can vary the device-level
electrical conductivity by orders of magnitude. We attribute this behavior to
the formation of filament-like conductive domains that percolate throughout the
system, { which form only when the electric conductivity depends on the
concentration}. We conclude by discussing the applicability of our results in
neuromorphic computing devices and Li-ion batteries.
