Triggered reversible phase transformation between layered and spinel structure in manganese-based layered compounds

Mi Ru Jo,Yong-Il Kim,Won-Sub Yoon,Junghoon Yang,Mihee Jeong,Yong-Mook Kang,Young-Min Kim,Maenghyo Cho,Kyeongse Song,Jin-Myoung Lim,Jae-Hyun Shim,Yunok Kim

doi:10.1038/s41467-019-11195-9

Abstract

Irreversible phase transformation of layered structure into spinel structure is considered detrimental for most of the layered structure cathode materials. Here we report that this presumably irreversible phase transformation can be rendered to be reversible in sodium birnessite (NaxMnO2·yH2O) as a basic structural unit. This layered structure contains crystal water, which facilitates the formation of a metastable spinel-like phase and the unusual reversal back to layered structure. The mechanism of this phase reversibility was elucidated by combined soft and hard X-ray absorption spectroscopy with X-ray diffraction, corroborated by first-principle calculations and kinetics investigation. These results show that the reversibility, modulated by the crystal water content between the layered and spinel-like phases during the electrochemical reaction, could activate new cation sites, enhance ion diffusion kinetics and improve its structural stability. This work thus provides in-depth insights into the intercalating materials capable of reversible framework changes, thereby setting the precedent for alternative approaches to the development of cathode materials for next-generation rechargeable batteries.

Highlights

Irreversible phase transformation of layered structure into spinel structure is considered detrimental for most of the layered structure cathode materials
From the Thermogravimetric analysis (TGA) profiles in Supplementary Fig. 2, hydrated Na-bir is estimated to have ~8 wt% of crystal water and its Na content reaches 6 wt% based on Inductively coupled plasmaatomic emission spectroscopy (ICP-AES) analysis (Supplementary Table 1), giving the formula Na0.27MnO2·0.54H2O
Raman spectroscopy (Fig. 1c) shows that hydrated Na-bir exhibits peaks at ~575–585 cm−1 and at ~640–650 cm−1 arising from the Mn–O bond stretching vibration in the basal plane of [MnO6] laminates

Summary

Introduction

Irreversible phase transformation of layered structure into spinel structure is considered detrimental for most of the layered structure cathode materials. We report that this presumably irreversible phase transformation can be rendered to be reversible in sodium birnessite (NaxMnO2·yH2O) as a basic structural unit This layered structure contains crystal water, which facilitates the formation of a metastable spinel-like phase and the unusual reversal back to layered structure. The mechanism of this phase reversibility was elucidated by combined soft and hard X-ray absorption spectroscopy with X-ray diffraction, corroborated by first-principle calculations and kinetics investigation These results show that the reversibility, modulated by the crystal water content between the layered and spinel-like phases during the electrochemical reaction, could activate new cation sites, enhance ion diffusion kinetics and improve its structural stability. The results here show that partial dehydration renders the Na-bir structure flexible, thereby enabling the reversible phase transformation between the layered and spinel-like structure

Objectives

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Conclusion