The origin of the synergetic effects of LFMP/LMO blend electrodes via dynamic in situ XRD analysis during cycling is explained. Blend electrodes are prepared by adding LiFe0.3Mn0.7PO4 (LFMP) and LiMn1.9Al0.1O4 spinel (LMO) in order to obtain a composite which utilizes the high capacity of LFMP and the rate capability of the spinel. Positive synergetic effects are observed for the electrochemical performance at high rates (3C), even exceeding theoretical calculations. A combined in situ X-ray diffraction (XRD) - electrochemistry cell is developed and tested during galvanostatic cycling. Its functionality is demonstrated by reproducing ex situ measurements from literature. A calibration curve of the spinel phase has been established in order to correlate the lattice parameter a to its depth of discharge (DoD). By concentrating only on the spinel component structural changes in blend electrodes during pulse power discharge at the manganese redox plateau can be investigated. During relaxation (I = 0), after a pulse has been applied, a shift in the XRD pattern can be observed indicating the partial re-charge of the spinel component by the LFMP. (C) The Author(s) 2016. Published by ECS. All rights reserved.