Mitigating the Ion Transport Tortuosity in Composite Cathodes of All-Solid-State Batteries by Wet Milling of the Solid Electrolyte Particles

Slow ion transport in the composite cathodes of bulk-type all-solid-state batteries (ASSBs) is one of the bottlenecks impeding the development of high-power batteries. In order to achieve high energy densities as well, the solid electrolyte volume fraction of composite cathodes should be in the range of 30% or below. Such low-volume fractions together with an inhomogeneous distribution of the solid electrolyte (SE) particles and poor particle contacts can give rise to high values for ion transport tortuosity in the cathode. Here, we show that an additional low-energy wet milling (LWM) step in the preparation of the SE particles reduces the mean particle size and the width of the particle size distribution considerably and leads to a more homogeneous distribution of the SE particles inside the composite cathode. Ion transport tortuosity measurements on symmetrical cells Li metal | solid electrolyte | composite electrode | solid electrolyte | Li metal show that after LWM, ion transport tortuosities as low as 8.0 are achievable at solid electrolyte volume fraction around 0.25 and that the obtained volume-fraction-dependent tortuosity values are close to those reported for conventional laboratory-scale lithium-ion batteries.