Achieving Slope-Reigned Na-Ion Storage in Carbon Nanofibers by Constructing Defect-Rich Texture by a Cu-Activation Strategy.

Hard carbons have shown promising application potential as anode materials for sodium-ion batteries (SIBs), but adjusting the texture of hard carbons to manipulate their electrochemical behaviors remains a great challenge. In this work, a Cu-activation strategy is developed to control the defects of hard carbon nanofibers to achieve slope-reigned Na-ion storage behaviors. This method can effectively create defect-rich carbon texture by employing a small amount of Cu(NO3)2 as an activator but cannot induce an increase in the surface area. With the addition of the Cu activator, carbon nanofibers with increasing defects are synthesized by electrospinning and subsequent annealing. When carbon nanofibers are used as anodes for SIBs, their reversible capacity is increased with the increase of defects. Simultaneously, slope capacity gradually increases, while low-voltage plateau capacity reduces. Especially, the reversible capacity of Cu-activated nanofibers with more defects can be increased to 315 mA h g-1 with almost no plateau capacity compared with 203 mA h g-1 of inactivated nanofibers with a plateau capacity of 26%. Noticeably, the initial Coulombic efficiency (70%) of the activated nanofibers is just slightly lower than that (72%) of inactivated ones. The Cu-activated nanofibers also demonstrate superb rate performance and long cycle lifetime. Therefore, this work shows a new pathway for the design of defect-rich hard carbons with superior Na-ion storage performance.