New anode materials for sodium-ion batteries: NixCa2-xAl-Cl LDH and CoyCa2-yAl-Cl LDH prepared from dechlorination wastes

Abstract

Layered double hydroxides (LDHs) are considered promising materials in energy storage. Herein, we design a one-step ion-exchange route to prepare two new LDH-based materials, NixCa2-xAl-Cl LDH and CoyCa2-yAl-Cl LDH as anode materials for sodium-ion batteries (SIBs), using Ca2Al(OH)6Cl·2H2O (Ca2Al-Cl LDH) generated from disposing of chlorine-containing wastewater as the feed material. The high-electroactive Ni2+ and Co2+ replace a part of low-electroactive Ca2+ in Ca2Al-Cl LDH, forming NixCa2-xAl-Cl LDH and CoyCa2-yAl-Cl LDH materials with tunnel-like and defective structure, and abundant active sites. Density functional theory calculations indicate that the incorporation of Ni2+ and Co2+ effectively drives electron transfer and directly influences the charge density surrounding the active center, thereby enhancing the conductivity of NixCa2-xAl-Cl LDH and CoyCa2-yAl-Cl LDH. Ex situ XRD and XPS analyses demonstrate a redox reaction between Na+ and NixCa2-xAl-Cl LDH/CoyCa2-yAl-Cl LDH during the discharging/charging process. The NixCa2-xAl-Cl LDH and CoyCa2-yAl-Cl LDH materials exhibit excellent electrochemical performance for SIBs. Among them, Ni0.8Ca1.2Al-Cl LDH and Co0.6Ca1.4Al-Cl LDH deliver discharge capacities of 256.9 and 292.8 mAh g−1 after 200 cycles at 0.2 A g−1 and maintain the discharge capacities of 102 and 118.1 mAh g−1 after 600 cycles at 2 A g−1. This study provides a simple and low-cost method to prepare LDH-based anode materials for SIBs. It also provides a new path for the conversion of low-value dechlorination wastes into high-value-added products.