Activation-Induced Turbostratic Ordering in pDCPD-Derived Hard Carbon Enables Stable Carbonate-Based Sodium-Ion...

Sodium-ion batteries are widely considered a promising alternative to lithium-ion batteries, due to the abundance and low cost of their raw materials. However, the development of high-performance and cost-effective electrode materials remains a significant challenge, particularly when competing with lithium iron phosphate systems. Herein, we present a hard carbon material derived from readily available poly(dicyclopentadiene) for use as a negative electrode in SIBs. This study investigates the influence of carbonization temperature and subsequent ${\mathrm{CO}}_2$ activation on the hard carbon structure and electrochemical performance. The impact of activation proved to be dependent upon the first stage carbonization temperature, creating greater local ordering for samples carbonized at higher temperatures. The removal of defects and increase in interlayer distance resulted in a turbostratic structure that enhanced rate performance and capacity retention when compared with non-activated samples. The optimized hard carbon exhibits a reversible capacity of 352 mAh  $g^{-1}$ at 0.1 C and a capacity retention of 88.1% after 500 cycles with a carbonate based electrolyte. This work introduces a cost-effective approach for producing hard carbon materials with distinctive nanostructure and provides valuable insights into achieving long cycle life in sodium-ion batteries.