A facile strategy toward sodium-ion batteries with ultra-long cycle life and high initial Coulombic Efficiency: Free-standing porous carbon nanofiber film derived from bacterial cellulose

Sodium-ion batteries (NIBs) has been considered as the most promising next generation low cost and environmentally friendly electrochemical energy storage system for smart-grid applications. To meet the requirements of practical application of NIBs, development the advanced carbon-based anode with both ultra-long cycle life and high initial Coulombic Efficiency (ICE) is one of the most critical challenges. Here, we realized free-standing and binder-free carbon nanofiber (CNFs) electrode with high ICE (93% at 0.2 A g(-1)) and long cycle life at high rate (105 mA h g(-1) at 10 A g(-1) after 10,000 cycles) by simply carbonization bacterial cellulose (BC) film. The carbonization temperature effects the local graphitic-like domains of carbon, resulting in the different electrochemical performance of the CNFs. The optimized carbonization temperature is 1300 degrees C. The study shows sodium ions could adsorption-co-intercalation of solvent and sodium ions in ether-based electrolytes, leading to high ICE and long cycle life at high rate capability. This approach not only provides a facile way for practical application of flexible NIBs but also paves a way to fabricate other flexible films for widely applications.