Solid-state Li-7 NMR studies of inverse spinel LiNixCo1-xVO4 cathode materials

Solid-state Li-7 NMR spectroscopy revealed different Ni/Co distributions in an inverse spinel structure of LiNixCo1-xVO4 cathode materials prepared by either a high-temperature solid-state reaction method (abbreviated as the HT method) or a low-temperature solution co-precipitation method (abbreviat ed as the LT method). Solid-state Li-7 NMR measurements confirmed that the lithium nuclear spin was dominated by a chemical shift anisotropy (CSA) int eraction compounded with a small second-order quadrupolar interaction. Ni/C o distribution and inhomogeneity of chemical shift tensors (delta(CSA) and eta(CSA) constants) associated with crystalline defects are accountable for the variation in spread of the MAS spinning side-band manifolds between ni ckel uptake and preparation methods. The NMR study also revealed that the H T method yielded broader Ni/Co distributions with greater lithium defects, while the LT method gave much more homogeneous Ni/Co distributions with sma ller defects. The NMR results were consistent with XRD data that showed a g radual expansion in the unit-cell lattice with increasing Co content. All c ells suffered a large irreversible loss in overall capacity in the first cy cle and became stable in terms of cycle efficiency during later cycling. We have found that LiNixCo1-xVO4 cathode materials prepared by the LT method with more homogeneous Ni/Co distribution and smaller crystalline defects of fer a small advantage in capacity over the HT method. (C) 2000 Elsevier Sci ence S.A. All rights reserved.