Ball-Milled Carbon Nano-Onions as High-Performance Conductive Additives for Zinc-Ion Batteries

Abstract Manganese dioxide (MnO2) cathodes for aqueous zinc-ion batteries (ZIBs) offer high capacity but suffer from poor electrical conductivity and sluggish kinetics. This study examines ball-milled carbon nano-onions (CNO-BMs) as high-performance conductive additives to address these challenges. We investigated the structural evolution of CNOs ball-milled for 2, 7, and 20 days. Results show that extended milling disrupts quaternary agglomerates (∼10 μm), reducing particle size to 280 nm while enhancing film conductivity from 3 S m−1 to 20 S m−1. When employed in MnO2 cathodes, the 20 day milled CNOs (CNO-BM20) outperform traditional Super P as a conductive additive. The CNO-BM20 cathode achieves a reversible capacity of 200 mAh g−1 at 0.1 A g−1, which is double that of Super P, and retains 80% of its capacity after 2000 cycles, significantly exceeding that of its commercial counterpart. Electrochemical analysis shows that the CNO network lowers charge-transfer resistance and exhibits higher GITT-derived apparent Zn2+ chemical diffusivity than Super P. These findings demonstrate that structurally engineered CNOs effectively unlock the potential of MnO2 for high-rate, durable aqueous energy storage.