A structural investigation of organic battery anode materials by NMR crystallography

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.

Rapid preparation of binary mixtures of sodium carboxylates as anodes in sodium-ion batteries

“…This idea is also supported by the 23 Na MAS and MQMAS spectra of Na-BDC (Fig. S18 and S22 †) where there is also a low-intensity third sodium site centred at approximately −25 ppm from the sodium atoms close to carboxylic groups in contrast with the two sites from Whewell et al 35 Such defects should not inuence the cycling performance when compared with the fully sodiated Na-BDC, as upon the rst charge-discharge cycle the H-atoms will be irreversibly exchanged for Na atoms. 22 The single carboxylate resonance (∼175 ppm) in the Na-BPDC 13 C CP MAS spectrum (Fig.…”

“…Elemental analysis for the binary mixtures confirmed the results estimated from the NMR fitting, with a slightly greater deviation for the mixture containing Na-BDC than the others although still within acceptable limits (Table S2†). When comparing the Na-BDC 13 C CP MAS NMR spectrum with that from Whewell et al 35 a second carboxylate resonance at approximately 173 ppm with lower intensity is observed possibly indicating that some of the H-atoms in the carboxylic groups are not fully exchanged for sodium atoms. This idea is also supported by the 23 Na MAS and MQMAS spectra of Na-BDC (Fig.…”

“…S15†) shows that the MW synthesis conditions used result in the production of the anhydrous phase of the Na-BPDC. 20,35…”

“…shows that the MW synthesis conditions used result in the production of the anhydrous phase of the Na-BPDC. 20,35 Working electrodes for all the materials were prepared using a water-soluble binder (10 wt%, carboxymethyl cellulose [CMC]), 60 wt% of active material (synthesised mixtures of sodium carboxylates) and conductive carbon (30 wt%). To gauge an initial response, cyclic voltammetry (CV) and galvanostatic cycling was performed for all mixtures and Na-(NDC)(MW) in half cells with sodium metal as the counter electrode.…”

Unveiling the topology of partially disordered micro-crystalline nitro-perylenediimide with X-aggregate stacking: an integrated approach

“…The multi-technique approach involves a combination of complementary techniques, including powder X-ray diffraction (PXRD), 3D ED, solid-state NMR and periodic density functional theory (DFT) calculations (Scheme 1 and Table S2 †) 27 for the structural characterization of materials on the atomic scale. [28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46] The central premise of the approach is to integrate local structural information available from NMR with information from different approaches, particularly exploiting complementary diffraction techniques such as PXRD and 3D ED, 47 which provide averaged information using the unit cell concept. The approach involves the following steps: (i) information from conventional chemical analysis techniques such as elemental analysis and solution NMR is used to determine the composition and chemical structure of the material.…”