Impact of Cathode Material Particle Size on the Capacity of Bulk-Type All-Solid-State Batteries

The implementation of all-solid-state batteries (ASSBs) is regarded as an important step toward next-generation energy storage systems, in particular for electric vehicles and portable electronics. This may be achieved through application of layered Ni-rich oxide cathode materials such as L1+x(Ni1-y-zCoyMnz)(1-x)O-2 (NCM) with high specific capacity and thiophosphate-based solid electrolytes. Here, the profound effect that the secondary particle size of the cathode active material has on the capacity of ASSB cells comprising NCM622 (60% Ni), beta-Li3PS4, and In anode is demonstrated. We show the benefits of using small particles (d << 10 mu m), allowing virtually full charge capacity. This finding is rationalized through galvanostatic charge-discharge tests and complementary ex situ and operando X-ray diffraction experiments combined with Rietveld refinement analysis. Our results indicate the importance of considering and avoiding electrochemically inactive electrode material in bulk-type ASSBs, which we show using charge transport measurements is due to poor electronic contact (in carbon-free cathode composites).