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OCT 27 2017

CIC energiGUNE seminar "Solid-State NMR: a Key Tool to Probe Local Structures, Electronic Structures and Defects in Battery Materials"

Speaker: Dr. Dany Carlier

From: CNRS, Univ. Bordeaux, Bordeaux & RS2E, Réseau Français sur le Stockage Electrochimique de l'Energie, Amiens, France

Magic Angle Spinning Nuclear Magnetic Resonance (MAS-NMR) is a very sensitive tool to probe local structures and local electronic structure of paramagnetic battery materials, thanks to the Fermi contact interaction. Indeed, the Fermi contact shift that predominates in paramagnetic compounds is due to the interaction between the nuclear spin and the surrounding unpaired electron spins. In order to assign the signals and understand the spin transfer mechanism through the chemical bonds, we have been developed the use of ab initio calculations for some years. A quantitative approach was achieved recently using either the WIEN2k code (FP-FLAPW) or the VASP code (PAW) to compute the electronic spin density on the probed nucleus; and the experimental magnetic susceptibilities. Our combined NMR/DFT studies of several tavorite-type AMPO4X (A = Li, H; M = Fe, Mn, V; X = O, F, OH) battery materials allowed to deeply understand the electronic structure of the materials.

 

Recently, using MAS-NMR we showed that several phosphate materials as LiVPO4F, or Na3V2(PO4)2F3, which are promising materials for positive electrode application in Li-ion and Na-ion batteries respectively, exhibit some defects. As these defects may affect the electrochemical behavior, their understanding is crucial.

In order to model diluted defect a PAW potential code (VASP) is preferred as a FP-LAPW one since it allow considering large supercells. The experimental signals assignment can thus be proposed and link to the local structure and electronic structure. In the two materials, we show that the defect is due to the substitution of some F atoms by O ones leading to the formation of V4+ ions locally. These V4+ ions are forming a vanadyl-type bond with the defect O, and affect the electrochemical cycling performances. Stoichiometric LiVPO4F, or Na3V2(PO4)2F3 phases could not be prepared so far making the MAS-NMR the most sensitive tool to probe the defects in these material. In a broader scope, these studies show the gain of combined NMR/DFT approach to understand battery materials.

Ending data: 10.27.2017
  • Place: CIC energiGUNE
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