The title compound, namely lithium cobalt(II/III) bis(diphosphate), Li(4.03)Co(1.97)(P(2)O(7))(2), is a new mixed-valent lithium/cobalt(II/III) phosphate. Three metal sites out of seven are occupied simultaneously by Li(+) and Co(II/III) ions. This disorder was established both from an analysis of the atomic displacement ellipsoids and Li/Co-O bond distances, and by means of a charge-distribution (CHARDI) model, which provides satisfactory agreement on the computed charges (Q) for all the cations.