posters 5th Asia-Pacific NMR Symposium 2013

Solid State NMR of Transition Metal Alloy-Modified LiMn2O4 for Composite Lithium-Ion Battery Cathode (#142)

Emmanuel I Iwuoha 1 , Natasha Ross 1 , Kenneth I Ozoemena 2 , Priscilla Baker 1
  1. SensorLab, University of Western Cape, CAPE TOWN, South Africa
  2. Council for Scientific and Industrial Research (CSIR), Pretoria, South Africa

The cathode of rechargeable lithium-ion batteries uses a transition metal oxide materials that can reversibly (de)intercalate lithium at a high potential difference. Manganese oxides cathode materials offer lower cost and lower toxicity than the normally used cobalt, and have been demonstrated to be safer on overcharge. However, LiMn2O4 exhibits capacity fading, Mn dissolution at high temperatures and poor high-rate capability compared to other cathode materials. Nano-alloy particles composed of Au with Pd and Pt metals were used to improve the electrocatalysis of the cathode materials by producing LiPdAu0.02Mn1.98O4 and LiPtAu0.02Mn1.98O4.7Li NMR spectroscopy was used to investigate the local structure of the manganese cathode materials after modification with Au and Pd or Pt nano-materials. Positive shifts seen in the LiPdAu0.02Mn1.98O4  solid state NMR spectra relative to LiMn2O4, are due to 180° interactions with half-filled eg orbitals. The lower intensity of the additional resonances observed for LiPdAu0.02Mn1.98O4 is consistent with the oxidation of fewer manganese ions; and the additional resonances were assigned to the lithium at  position 8a of the spinel LiMn2O4 structure in accordance to the Fermi contact shift mechanism. A single isotropic resonance at the high frequency region indicates that Li atoms are near the Mn (IV) cations. This phenomenon can be explained by the changes in the distance or nuclear charges within the lithium  and neighboring atoms.  The manganese present as Mn4+ in this material acts as an inert spectator ion, however due to the presence of PdAu in the spinel, PdAu-Li+ exchange occurred between the neighboring atoms in the spinel allowing the  detection of  Li+ ions. The corresponding NMR data for LiPtAu0.02Mn1.98O4 will be presented and all NMR results will be complemented with XRD, FTIR and cyclic voltammetric data for the materials.