Rational electrode design for balanced and enhanced ionic and electronic conduction in high-loading all-solid-state batteries

• The CNT-coated cathode materials are utilized for an effective electrode design. • The composite electrode with CNT-coated cathode simultaneously improves ionic and electronic conduction. • Under optimized conditions, the electrode with a loading level of 153 mg/cm 2 achieves a capacity of 12.7 mAh/cm 2 . Balanced ionic and electronic conduction within the electrode is essential for efficient electrochemical reactions in battery systems. In particular, all-solid-state electrodes require more precise and sophisticated designs to optimize conduction due to the use of bulky solid electrolyte particles for lithium-ion transport, unlike liquid electrolytes that conformally wet solid components. In this context, the limited remaining space, apart from the active material particles, must be effectively utilized to achieve superior ionic and electronic conduction. Herein, we propose a straightforward composite electrode design in which carbon nanotubes with high electronic conductivity are directly coated onto the surface of cathode materials to address these challenges. While conventional composite electrodes with randomly mixed structures of carbon black and solid electrolytes suffer from transport interruptions between charge carriers, this design facilitates electronic conduction at the interface between the active material and the solid electrolyte domains. Consequently, each charge carrier is transported without significant interruption, resulting in higher ionic and electronic conduction compared to conventional composite electrodes. Moreover, the efficient utilization of the electro-conductive agent significantly reduces its required amount to as low as 0.07 wt% of the total electrode weight, offering additional design flexibility for active materials and increasing electrode density. Thanks to these advantages, all-solid-state electrodes with an ultrahigh loading of 153 mg/cm 2 can achieve a capacity of 12.7 mAh/cm 2 , presenting a practically meaningful pathway toward realizing high-loading all-solid-state batteries.