Engineering Stress-Release Structures Based on Biological Swelling in Carbon Fibers for Stable Sodium Ion Storage

Benefiting from the high abundance and uniform distribution of sodium, sodium ion batteries hold great potential as an alternative to lithium ion batteries. However, developing stable commercialized carbon anodes remains a challenge due to the high accumulated stress associated with the drastic volume change during sodium ion insertion/extraction. Based on the finite element simulations, the von Mises stress distributions reveal the critical role of the radial porosity in stress accumulation and strain relaxation. Herein, radial porous carbon fibers (PCFs) are synthesized using a green and facile strategy based on biological swelling and dynamic graphitization. According to the finite element simulation results, PCF anodes display excellent stability for long-term cycling at a high current density. Owing to the super charge transportation and sodium ion diffusion dynamics (9.2 × 10-13 cm2 s-1), PCF anodes deliver a high reversible capacity of 213 mA h g-1 after 1000 cycles at 0.5 A g-1. This work provides an insight to improve the electrochemical performance of micron-sized carbon anode materials for storing alkali metal ions with a large ionic radius.