The possibility of metal reduction during the charging of secondary lithium batteries with LixMO2 cathodes is investigated. Loss of active material due to metal reduction can be one of the causes of capacity decay in these batteries after repeated charging. First principles methods are used to calculate the metal reduction potentials in layered LixMO2 compounds where M = Ti, V, Mn, Fe, Co or Ni. It is found that, for several of these compositions, the metal ions may preferably reduce before the lithium ion during charging.