A structural investigation of organic battery anode materials by NMR crystallography.

Tommy Whewell,Russell E Morris,John M Griffin,Aamod V Desai,Nathan R Halcovitch,Valerie R Seymour,A Robert Armstrong,Kieran Griffiths

doi:10.1002/mrc.5249

Tommy Whewell, Russell E Morris + Show 6 more

Open Access

https://doi.org/10.1002/mrc.5249

Copy DOI

Abstract

Conjugated alkali metal dicarboxylates have recently received attention for applications as organic anode materials in lithium- and sodium-ion batteries. In order to understand and optimise these materials, it is important to be able to characterise both the long-range and local aspects of the crystal structure, which may change during battery cycling. Furthermore, some materials can display polymorphism or hydration behaviour. NMR crystallography, which combines long-range crystallographic information from diffraction with local information from solid-state NMR via interpretation aided by DFT calculations, is one such approach, but this has not yet been widely applied to conjugated dicarboxylates. In this work, we evaluate the application of NMR crystallography for a set of model lithium and sodium dicarboxylate salts. We investigate the effect of different DFT geometry optimisation strategies and find that the calculated NMR parameters are not systematically affected by the choice of optimisation method, although the inclusion of dispersion correction schemes is important to accurately reproduce the experimental unit cell parameters. We also observe hydration behaviour for two of the sodium salts and provide insight into the structure of an as-yet uncharacterised structure of sodium naphthalenedicarboxylate. This highlights the importance of sample preparation and characterisation for organic sodium-ion battery anode materials in particular.

Highlights

In recent decades, batteries have held an increasing importance in everyday life
We present a systematic study of model organic anode materials for lithium and sodium batteries using NMR crystallography
We find that the choice of optimisation method can have a measurable effect on the unit cell parameters and atomic positions from the point of view of Powder X-ray diffraction (PXRD) but that, in most cases, the effect on the local structure is small and calculated NMR parameters are relatively insensitive to the optimisation method used

Summary

Introduction

Lithium-ion batteries are well established in society with a growing focus on green-tech applications, including electric vehicles, and demand is set to increase further. As their usage increases, there are concerns surrounding the ethics and sustainability of the raw materials used, which is driving development of new battery chemistries. One aspect concerns the development of new chemistries based on more sustainable charge carrying ions such as sodium, which is seen as a low-cost alternative to lithium due to its much higher abundance Another goal is to increase the sustainability of other aspects of battery chemistry.

Objectives

Methods

Results

Conclusion