Abstract
Abstract
Cell components that enable high energy density, the reduction of operation pressure, and the adaptation of established production processes are important for the breakthrough of Li-ion all-solid-state batteries (ASSBs). Slurry-based processing, adapted from Li-ion battery technology, represents a promising production route. Although slurry-based fabrication of separators has been reported, the influence of the operation pressure on their conductivity and the effect of the mechanical properties of the polymer binder in composite separators remains elusive. Here we report a slurry-based process to obtain free-standing solid electrolyte (SE)/binder composite sheets as ASSB separators, employing different contents and types of binder. Using electrochemical impedance spectroscopy, we investigate their ionic conductivity as a function of fabrication pressure (yielding different separator porosities) and operation pressure. Using a novel cell-setup approach, we quantify the conductivity loss for fully densified composite SE/binder-sheets when measured at practically relevant, reduced operation pressures, comparing it with the maximum conductivity attained at very high operation pressures. The conductivity loss is related to a “springback” effect, whereby the pressure release after fabrication leads to a volumetric expansion of the polymer phase, resulting in decreased ionic conductivity. The extent of this effect strongly depends on both the type of binder and its content.