Double Perovskites: Promising Positive Electrode Materials for Potassium Ion Batteries

Abstract

The popularity of electric vehicles over the last decade has led to a boom in lithium-ion battery production. Large amounts of lithium resources have been consumed resulting in a lithium shortage.[1] To overcome the challenge of excessive consumption of lithium resources, alternative battery technologies to Li-ion batteries must be considered. Potassium-ion batteries (KIBs) have been proposed as an alternative battery technology to Li-ion batteries and are at the early stage of development.This study focuses on investigating the viability of employing the novel double-perovskites as positive electrodes for KIBs. Double perovskites have some structural similarities to the well-developed KIB positive electrode materials, Prussian White or Prussian Blue Analogues. The 3D open framework is favorable for supporting the insertion/deinsertion of K-ions and K-ion diffusion. In this research, new double-perovskites have been successfully synthesized using the solid-state methods, under both inert and reducing atmospheres. The utilization of choice of transition elements on the B-site in the perovskite structure is beneficial for increasing energy density, enhancing electronic conductivity, and improving the structure stability of the material. Preliminary characterization, including powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS), were conducted to verify the phase purity, crystal structure, and atomic ratio of different elements in the synthesized material.At the same time, electrochemistry tests were conducted by cycling the perovskite in half-cells, revealing an irreversible capacity decay in the first cycle. To further investigate structural changes of the perovskite during cycling, operando X-ray absorption spectroscopy (XAS) was employed. This method enabled the study of the oxidation states of the transition metals in the perovskites, providing advanced insights into the redox reactions occurring within cells with positive electrodes.Obtaining a detailed understanding of the structure of these perovskites is crucial. Thus, powder neutron diffraction (PND) and variable temperature neutron diffraction (VT-PND) have been gathered to study the structural evolution, site occupancy and octahedral tilting with upon heating in both inert and reducing atmospheres.Reference:[1] AP News, https://apnews.com/article/china-ev-lithium-united-states-battery-87eb9382a0181bb7ee64e835efe7b170, (accessed December 2023).