The poor electrochemical performance of LiMnPO4 nanoplates relative to that of isostructural LiFePO4 is clarified. LiMnPO4 nanoplates ca. 2 mm in diameter and 50 mm thick were prepared by a single solvothermal method. The [010] 1D Li+ diffusion path lies in the plane of the platelets, and the two-phase LiMnPO4/MnPO4 interface intersects the [010] direction. A 10% volume change and a cooperative Jahn-Teller distortion of the Mn3+ sites in the MnPO4 phase introduces a large strain across the interface that impedes the rate of interface motion and therefore the rate of Li extraction/insertion. Nevertheless, a capacity of 107.5 mAh g−1 at the C/20 rate had a capacity fade of only 0.08% per cycle LiFePO4 platelets, on the other hand, have the [010] 1D Li+ diffusion paths perpendicular to the platelets and the LiFePO4 interface parallel to the [010] direction, which leaves short diffusion lengths that are not blocked by structural changes.