Bulk-type all-solid-state batteries with mechanically prepared LiCoPO4 composite cathodes

All-solid-state Li batteries are suitable for the application of 5 V-class cathode materials that can provide high energy densities. However, it is hard to fabricate bulk-type batteries composed of a mixture of active materials and solid electrolytes because of the difficulty of ensuring a conductive path and suppressing the formation of reactive layers at the interface. Herein, we report a simple mechanical processing route to composite cathode granules synthesized from a 5 V-class LiCoPO4 cathode, conductive carbon, and phosphate solid electrolyte. The homogeneously dispersed component particles were granulated during the mechanical treatment. The first discharge capacity is 82 mAh/g for the bulk-type all-solid-state battery obtained by using a composite cathode pellet, polymer solid electrolyte, and Li anode. Scanning transmission electron microscope-electron energy loss spectroscopy measurements did not reveal any Co diffusion or the formation of a resistive layer at the interface between LiCoPO4 and the solid electrolyte. The fabrication of a composite cathode by mechanical treatment is essential for the development of high-energy bulk-type all-solid-state batteries.