Here a series of Al-doped LiMnPO4 with controlled cation ratios based on appropriate charge compensation mechanisms are synthesized and compared. The results suggest that Al3+ can be doped into the lattice of LiMnPO4 and the preferable doping mechanism is in a scheme of Li1-xAlxMnPO4 where Al3+ occupies Li+ site with charge compensation by electronic defect. Such a charge-compensation mechanism is much different from those previously reported and needs further study. (C) 2019 The Electrochemical Society.