Impact of Pore Size in Structurally Controlled Carbon Black Interlayers on the Performance of Anode-less All-Solid-State Batteries

Abstract

The advancement of all-solid-state batteries (ASSBs) as a safer and higher-performance alternative to traditional lithium-ion batteries (LIBs) has garnered significant attention, particularly in addressing challenges related to lithium dendrite formation. This study explores the role of carbon interlayers in anode-less ASSBs, focusing on how the structural characteristics of carbon black and pore size affect lithium diffusion, plating morphology, and electrochemical performance. It examines how variations in aggregate structure and pore size distribution influence lithium interface diffusion rate and overall battery performance by comparing three types of carbon black, Li-250, Super P and ECP-300J, which share the same primary particle size but differ in aggregate structural complexity. High-structure carbon black, ECP-300J, demonstrated the smallest average pore size of 23.3 nm, created through numerous intra-aggregate pores, which improved lithium diffusion rates and enabled uniform lithium plating. This led to the highest critical current density (CCD) of 7.6 mA/cm² and a prolonged cycle life exceeding 300 hours at a current density of 0.5 mA/cm². In contrast, low-structure carbon black, Li-250, with larger pore sizes of 45.6 nm, showed slower lithium diffusion, uneven plating, and the shortest cycle life due to localized lithium accumulation. Super P, with a moderate pore size of 34.6 nm, struck a balance between diffusion efficiency and structural stability but performed less effectively than ECP-300J. Electrochemical analysis revealed that smaller pore sizes promote higher lithium diffusion efficiency and improved interfacial stability by reducing charge transfer resistance and enabling more uniform lithium transport. SEM and TEM observations confirmed that optimized pore size distribution and structural control significantly impact lithium plating morphology, with ECP-300J forming the densest and most uniform lithium layers. Furthermore, dynamic light scattering (DLS) and BET analyses demonstrated how dispersion processes, including ball milling and ultrasonication, influence aggregate breakdown and pore size formation. This study highlights the critical importance of designing carbon interlayers with controlled pore sizes and structural properties to enhance lithium diffusion, improve uniform plating, and achieve superior electrochemical performance in ASSBs. These findings provide a foundational understanding for optimizing interlayer design in next-generation energy storage systems.