LiNiPO4–LiCoPO4 solid solutions were investigated as potential cathodes for use in Li-ion batteries. Cyclic voltammetry and discharge curves reveal that the discharge capacity of the LiNiPO4–LiCoPO4 solid solutions is associated entirely with the Co3+/Co2+ redox couple at a potential of 4.7–4.8V. The effect of Ni is to reduce the length of the 4.7–4.8V plateau.