Lithium and sodium insertions into pyrophosphates MP2O7 (M = Mo, W) were investigated electrochemically as possible cathodes for ion-transfer batteries. Lithium and sodium were reversibly incorporated in the 3D-framework of pyrophosphates MP2O7 (M = Mo, W) with liquid organic electrolytes at room temperature. The first discharge capacities were 95 mAhg-1 for A1.0MoP2O7 (A = Li, Na) and 295 mAhg-1 for A4.0WP2O7 (A = Li, Na), respectively. The guest (Li or Na) insertion into WP2O7 induced a transition to the amorphous phase, whereas the insertion into MoP2O7 proceeded topotactically with a smooth single phase reaction.
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