The synthesis of a new anhydrous sodium manganese oxide alpha-Na0.66MnO2.13 obtained via a sol-gel process in organic medium is reported. The partial and limited removal of sodium ions from the layered host lattice (hexagonal symmetry; a = 2.84 angstrom, c = 11.09 angstrom) allows to get a high and stable specific capacity of 180 mAh g(-1) at C/20 in the cycling limits 4.3/2 V with a mean working voltage of 3 V without the emergence of a spinel phase. By introducing acetylene black in solution during the sol-gel reaction, a composite material containing 8 wt.% AB has been obtained. The rate capability is shown to be significantly improved leading to an increase of the available specific capacity with for instance 200 and 90 mAh g(-1) at C/20 and C rate. This effect is ascribed to a better electronic contact between particles and/or the modification of the oxide surface which makes the intercalation process more homogeneous and more efficient. (c) 2006 Elsevier Ltd. All rights reserved.