Alkali-independent Anion Redox in LiNaFeS2

15 May 2024, Version 1
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

Although Na-ion batteries present a promising and more sustainable solution compared to Li-ion batteries, Na-ion batteries have comparatively lower energy density and suffer from irreversible charge storage due to the size and mass of Na+. In recent years, the investigation of Li-rich materials has revealed employing multielectron redox that couples cation and anion redox is a method to improve capacity. Coupling anion and cation redox could be a way to improve the low energy density of Na-ion cathodes, but the influence of the large Na+ on these electrochemical processes is not well understood. Here, we leverage the mixed-alkali nature of LiNaFeS2 to compare its behavior in Li vs. Na half cells. LiNaFeS2 is known to support multielectron redox by virtue of cation and anion redox in Li half cells. We now demonstrate that LiNaFeS2 can also be used as a multielectron Na cathode. Elemental analysis of the cathodes at various states of charge verify Na as the dominant mobile ion after first charge, which correlates to different structural responses that cause deviations in the electrochemistry compared to the material cycled in a Li half cell. Notably, cycling with a Na electrolyte causes the particles to roughen and amorphize. Fe and S K-edge X-ray absorption spectroscopy show that the charge compensation mechanisms from an electronic structure point of view are fundamentally the same independent of cell configuration. The disparate electrochemical behavior is entirely due to structural rather than electronic effects, which is further probed with synchrotron X-ray diffraction studies, scanning electron microscopy, and cyclic voltammetry coupled with b-value analysis. Our work provides a fundamental study on the differences between Li- and Na-based anion redox in the same material.

Keywords

Na ion cathodes
anion redox
persulfide

Supplementary materials

Title
Description
Actions
Title
Supporting Information for: Alkali-independent Anion Redox in LiNaFeS2
Description
Synchrotron XRD, long term cycling data, Fe K-edge XAS, ex situ SEM and EDS
Actions

Comments

Comments are not moderated before they are posted, but they can be removed by the site moderators if they are found to be in contravention of our Commenting Policy [opens in a new tab] - please read this policy before you post. Comments should be used for scholarly discussion of the content in question. You can find more information about how to use the commenting feature here [opens in a new tab] .
This site is protected by reCAPTCHA and the Google Privacy Policy [opens in a new tab] and Terms of Service [opens in a new tab] apply.