Electrochemically Active Molybdenum Phosphate with Open‐Framework Structure

Somewhat less investigated, lithium ion containing molybdenum phosphate compounds are synthesized via simple template free hydrothermal method. Single‐crystal X‐ray diffraction (SCXRD) study reveals that the compounds Li 0.89 Mo 2 O 1.89 F 0.11 (PO 4 ) 2 (H 2 PO 4 )· x H 2 O ( x ≈1) and Li 3 Mo 2 O 2 (PO 4 ) 3 · x H 2 O ( x ≈1) crystallize in monoclinic C 2/ m and C 2/ c space group, respectively. The structures are built of alternate corner‐sharing of MoO 6 octahedra and PO 4 tetrahedra forming layers, which are pillared by phosphate groups creating a 3D framework with channels. These channels host Li‐ions and have the potential for further intercalation of alkali ions. When heated at 200 °C, both the compounds go through structural rearrangements due to the removal of crystal water which results in an anhydrous phase with the same structural arrangement. When studied as Li‐ion intercalation cathode, the anhydrous phase of Li 0.89 Mo 2 O 1.89 F 0.11 (PO 4 ) 2 (H 2 PO 4 )· x H 2 O ( x ≈1) achieves 79.36 mAh g − 1 capacity upon charging corresponding to the removal of ≈1 Li ion from the structure. The subsequent discharge capacity corresponds to 2.88 moles of Li ion insertion to the structure. Additionally, Na ions could be reversibly intercalated when cycled between 1.5 and 4 V. Besides electrochemistry, Fourier‐transformation infrared, X‐ray photoelectron spectroscopy, and thermogravimetric analysis are performed to confirm the presence of water and thermal stability of the materials.