Revealing defects in crystalline lithium-ion battery electrodes by solid state NMR: applications to LiVPO4F

Robert J. Messinger (1, 2) , Michel Ménétrier (2, 3, 4) , Elodie Salager (2, 1) , Adrien Boulineau (5) , Mathieu Duttine (4) , Dany Carlier (2, 4) , Jean-Marcel Ateba Mba (3, 4, 6) , Laurence Croguennec (2, 3, 4) , Christian Masquelier (2, 3, 6) , Dominique Massiot (1) , Michaël Deschamps (1, 2)

1 CEMHTI - Conditions Extrêmes et Matériaux : Haute Température et Irradiation
2 RS2E - Réseau sur le stockage électrochimique de l'énergie
3 ALISTORE-ERI - Advanced Lithium Energy Storage Systems - ALISTORE-ERI
4 ICMCB - Institut de Chimie de la Matière Condensée de Bordeaux
5 LITEN - Laboratoire d'Innovation pour les Technologies des Energies Nouvelles et les nanomatériaux
6 LRCS - Laboratoire réactivité et chimie des solides - UMR CNRS 7314 UPJV

Identifying and characterizing defects in crystalline solids is a challenging problem, particularly for lithium-ion intercalation materials, which often exhibit multiple stable oxidation and spin states as well as local ordering of lithium and charges. Here, we reveal the existence of characteristic lithium defect environments in the crystalline lithium-ion battery electrode LiVPO4F and establish the relative subnanometer-scale proximities between them. Well-crystallized LiVPO4F samples were synthesized with the expected tavorite-like structure, as established by X-ray diffraction (XRD) and scanning transmission electron microscopy (STEM) measurements. Solid-state 7Li nuclear magnetic resonance (NMR) spectra reveal unexpected paramagnetic 7Li environments that can account for up to 20% of the total lithium content. Multidimensional and site-selective solid-state 7Li NMR experiments using finite-pulse radio frequency-driven recoupling (fp-RFDR) establish unambiguously that the unexpected lithium environments are associated with defects within the LiVPO4F crystal structure, revealing the existence of dipole–dipole-coupled defect pairs. The lithium defects exhibit local electronic environments that are distinct from lithium ions in the crystallographic LiVPO4F site, which result from altered oxidation and/or spin states of nearby paramagnetic vanadium atoms. The results provide a general strategy for identifying and characterizing lithium defect environments in crystalline solids, including paramagnetic materials with short 7Li NMR relaxation times on the order of milliseconds.

Domains: Material chemistry

Robert J. Messinger, Michel Ménétrier, Elodie Salager, Adrien Boulineau, Mathieu Duttine, et al.. Revealing defects in crystalline lithium-ion battery electrodes by solid state NMR: applications to LiVPO4F. Chemistry of Materials, 2015, 27 (15), pp.5212-5221. ⟨10.1021/acs.chemmater.5b01234⟩. ⟨hal-01200997⟩