Composite Cathode Material Using Spark Plasma Sintering for Bulk-Type Hybrid Solid-State Batteries

A Composite cathode without polymer binder was prepared by a one-step sintering method employing spark plasma sintering (SPS) of laminated LiCoO₂ and Li₃BO₃ pellets. The amorphous Li₃BO₃ solid electrolyte melted during the sintering process. For better characterization of the composite cathode, a liquid electrolyte was used in the battery test. However, the active material was mainly in the all-solid-state environment. The specific capacity of the composite cathode was found to be dependent on its thickness. The 0.2 mm thick composite cathode showed a high specific discharge capacity of 99 mAh g ⁻¹ at 0.5 C rate, excellent cycling performance over 10 cycles, and good rate capability of about 93.2 mAh g ⁻¹ with 94% retention capacity. In addition, the composite cathode showed an initial discharge capacity of 0.25 mAh g ⁻¹. The discharge capacity after 3 cycles under the all-solid-state condition was 0.22 mAh g ⁻¹. The SEM and TEM results showed that the melted Li₃BO₃ solid electrolyte synthesized by the SPS process produced Li+ ion transport pathways, which reduced the grain boundary resistance. Hence, this composite cathode consisting of LiCoO₂ as the cathode, amorphous Li₃BO₃ as the solid electrolyte, and MWCNT as the electric conductor is a promising material for all-solid-state batteries and bulk-type hybrid solid-state batteries.