Layered double hydroxides as high-performance anode material for potassium ion battery

Abstract In recent years, potassium ion batteries (PIBs) with capacitor-like rate performance and battery-like capacity are highly desirable. To this aim, layered double hydroxides (LDHs) are studied in this work to evaluate the feasibility of employing LDHs as anode materials for PIBs. Our results show MgFe-LDH that contains trivalent iron cations with variable valence states can deliver K+-storage capacity of 371.6 mAh g–1 after running for 300 cycles at 0.1 A g–1 with an initial Coulombic efficiency of 88.4%. In contrast, MgAl-LDH that represents LDHs excluding multivalent metal elements merely delivers a capacity of 195.3 mAh g-1 under the same test condition but with a much higher initial Coulombic efficiency of 99.4%. Further study shows an electrical double layer effect is dominant to storing K+ for MgAl-LDH anode, while a faradaic process involving a conversion reaction between Fe3+ and Fe2+ is prevalent in MgFe-LDH anode. Rate performance of the MgFe-LDH/K cell shows its capacity retentions at 1, 2, 5, 10 A g–1 are 60.9%, 51.3%, 42.9%, 39.5%, respectively, which exhibit cause-effect relationships with its intrinsic poor conductivity and a non-efficient grinding event at high current densities. Besides, by measuring EIS spectra at different temperatures, the apparent activation energy is calculated to be 79.5 kJ mol–1. It is thus anticipated that this study will shed new light on developing LDHs as powerful anode materials for PIBs.