Expanded mesocarbon microbead cathode for sodium-based dual-ion battery with superior specific capacity and long-term cycling stability

Dual-ion batteries (DIBs) have attracted tremendous attention owing to their high operating voltage and are considered promising candidates for low-cost clean energy storage devices. However, the decomposition of electrolytes and collapse of the cathode structure may lead to low Coulombic efficiency (CE) and low cycling stability of DIBs. Wide-layered electrode materials can accommodate the intercalation/deintercalation of large anions, which is believed to overcome these issues. Herein, expanded mesocarbon microbeads (200HRO-MCMB) possessing an enlarged interlayer spacing (0.405 nm) were prepared via modified Hummers and subcritical hydrothermal reduction methods. After the indispensable electrochemical activation, 200HRO-MCMB (hydrothermal reduction at 200 °C) exhibited a high specific capacity (120 mAh·g⁻¹ at 50 mA·g⁻¹) when used as a cathode for a sodium-based DIB, and the CE significantly improved within the 2.0–4.5 V voltage range. Additionally, the cycling stability exceeded over 600 cycles. Remarkably, this cathode possessed enlarged interlayers that decreased the barrier of PF₆⁻ transport, and the battery storage mechanism corresponded to a transitioning state between double-layer capacitance and Faradaic intercalation. Undoubtedly, this work will expand the scope of the practical application of low-cost sodium-based DIBs.