Binder‐Free Self‐Standing Hard Carbon Electrodes Graphite‐Coated by PE‐CVD to Boost the Efficiency of Na‐Ion Batteries

This work explores the use of plasma‐enhanced chemical vapor deposition (PE‐CVD) to deposit a C‐coating on binder‐free, self‐standing electrodes (SSEs). The C‐coating consists of a nanocrystalline graphite thin film with crystalline domains measuring ≈14 nm. Regardless of the fabrication pyrolysis temperature of SSE, an increase in crystallite size and a reduction in interlayer space and defects is observed after C‐coating and post‐treatment at 1500 °C. Pyrolysis of the SSE at 900 °C induce better coverage with the nanographitic layer during PE‐CVD , but prevents the development of closed pores during post‐treatment at 1500 °C. In contrast, a large number of closed pores form when the SSE is pyrolyzed at 1500 °C. However, no difference in performance is observed between the C‐coated SSE pyrolyzed at 900 and 1500 °C and post‐annealed at 1500 °C, therefore, lower temperature can be advantageously used for the pyrolysis step. Nevertheless, post‐treatment at 1500 °C is necessary to enhance performance. For both materials, the graphite coating minimized the undesirable reactions with the electrolyte, leading to more stable and conductive solid electrolyte interphase, which improves iCE (from 91.0% to 92.5%). A high reversible capacity of 320 mAh g −1 is also obtained, and the higher coating's conductivity is beneficial for rate capability.