Rechargeable, all-solid-state Li ion batteries (LIBs) with high specific
capacity and small footprint are highly desirable to power an emerging
class of miniature, autonomous microsystems that operate without a
hardwire for power or communications. A variety of three-dimensional
(3D) LIB architectures that maximize areal energy density has been
proposed to address this need. The success of all of these designs
depends on an ultrathin, conformal electrolyte layer to electrically
isolate the anode and cathode while allowing Li ions to pass through.
However, we find that a substantial reduction in the electrolyte
thickness, into the nanometer regime, can lead to rapid self-discharge
of the battery even when the electrolyte layer is conformal and pinhole
free. We demonstrate this by fabricating individual, solid-state
nanowire core–multishell LIBs (NWLIBs) and cycling these inside a
transmission electron microscope. For nanobatteries with the thinnest
electrolyte, ≈110 nm, we observe rapid self-discharge, along with void
formation at the electrode/electrolyte interface, indicating electrical
and chemical breakdown. With electrolyte thickness increased to 180 nm,
the self-discharge rate is reduced substantially, and the NWLIBs
maintain a potential above 2 V for over 2 h. Analysis of the
nanobatteries’ electrical characteristics reveals space-charge limited
electronic conduction, which effectively shorts the anode and cathode
electrodes directly through the electrolyte. Our study illustrates that,
at these nanoscale dimensions, the increased electric field can lead to
large electronic current in the electrolyte, effectively shorting the
battery. The scaling of this phenomenon provides useful guidelines for
the future design of 3D LIBs.
capacity and small footprint are highly desirable to power an emerging
class of miniature, autonomous microsystems that operate without a
hardwire for power or communications. A variety of three-dimensional
(3D) LIB architectures that maximize areal energy density has been
proposed to address this need. The success of all of these designs
depends on an ultrathin, conformal electrolyte layer to electrically
isolate the anode and cathode while allowing Li ions to pass through.
However, we find that a substantial reduction in the electrolyte
thickness, into the nanometer regime, can lead to rapid self-discharge
of the battery even when the electrolyte layer is conformal and pinhole
free. We demonstrate this by fabricating individual, solid-state
nanowire core–multishell LIBs (NWLIBs) and cycling these inside a
transmission electron microscope. For nanobatteries with the thinnest
electrolyte, ≈110 nm, we observe rapid self-discharge, along with void
formation at the electrode/electrolyte interface, indicating electrical
and chemical breakdown. With electrolyte thickness increased to 180 nm,
the self-discharge rate is reduced substantially, and the NWLIBs
maintain a potential above 2 V for over 2 h. Analysis of the
nanobatteries’ electrical characteristics reveals space-charge limited
electronic conduction, which effectively shorts the anode and cathode
electrodes directly through the electrolyte. Our study illustrates that,
at these nanoscale dimensions, the increased electric field can lead to
large electronic current in the electrolyte, effectively shorting the
battery. The scaling of this phenomenon provides useful guidelines for
the future design of 3D LIBs.