The Li-7 NMR T-1 spin-lattice relaxation time is shown to be a very stringent criterion for determining the stoichiometry of LiCoO2. When Co3O4 containing a minimum impurity level of paramagnetic ions such as Fe or Ni is used as the starting material (together with Li2CO3), a T-1 value as long as 18 s is obtained, but this requires a rather long thermal treatment for complete elimination of excess Li. Such highly stoichiometric Li1CoO2 exhibits a very early insulator to metal transition upon Li deintercalation. Magnetic susceptibility and specific heat capacity investigations show the exclusive presence of diamagnetic low-spin (LS) Co3+. (C) 2008 The Electrochemical Society.