Eucommia Ulmoides Barks-derived Anodes for Sodium ion Battery and Method to Improve Electrochemical Performances by Modifying Defects

Hard carbon were prepared from Eucommia ulmoides barks by carbonization (1100 or 1300 °C) and then used as anode materials for sodium ion battery (SIB). Results showed that, although increased carbonization temperature had positive influence on the initial coulombic efficiency (ICE) of samples, the sample carbonized at higher temperature could not show higher specific capacities from 100 mA g^− 1 to 1 A g^− 1 (current density). This phenomenon could be attributed to few changes of specific surface area for samples carbonized at different temperature. Further studies showed that if the obtained hard carbon underwent high temperature treatment together with pitch powders (the hard carbon did not need to contact with pitch powders directly during the treating process), the specific surface area of samples decreased, while number of disordered bonds and interlayer distance of crystallites increased. The modification of structural defects made the samples show better electrochemical performances (ICE, specific capacity and cycling characteristic). Additionally, when the method (modifying defects) was used in Cupressus funebris (cypress wood) based anodes for SIB, the ICE and specific capacities at different current densities of samples could also be improved, which means the method may have good applicability for producing biomass-derived SIB anodes on a large scale.

Graphical Abstract