Li2+x Mn1−x P x Si1−x O4 are prepared by a sol–gel method and characterized as novel cathode materials for lithium ion batteries. Single-phase Li2+x Mn1−x P x Si1−x O4 can be obtained when x is equal to 0, 0.05 and 0.1 and the calcination temperature is 700°C. Calcining at 900°C is of no avail to prepare single-phase Li2+x Mn1−x P x Si1−x O4. In contrast to Li2MnSiO4 and Li2.1Mn0.9P0.1Si0.9O4, Li2.05Mn0.95P0.05Si0.95O4 has nearly the same structure at both calcination temperatures. The Li2.05Mn0.95P0.05Si0.95O4/C sample calcined at 700°C has the best electrochemical performance among the three single-phase samples, which is in accordance with the fact that it has the lowest charge transfer resistance. Smaller particle size and larger specific surface area are obtained at higher x value, and all the Li2+x Mn1−x P x Si1−x O4/C (x =0, 0.05 and 0.1) samples have a core–shell structure. The calcination temperature of 700°C is the best between 600 and 800°C in consideration of both phase purity and crystallinity, resulting in the highest discharge capacity of Li2.05Mn0.95P0.05Si0.95O4.