The new compound Li1.65Na0.35Fe[PO4]F with the Li2Ni[PO4]F structure has been prepared from the analogous LiNaFe[PO4]F phase by ion exchange using LiBr in ethanol at 90 degrees C. The sample was characterized by powder X-ray diffraction, Fe-57 Mossbauer spectroscopy, and electrochemical measurements. Li1.65Na0.35Fe[PO4]F crystallizes with orthorhombic symmetry, space group Prima, with a = 10.5093(5) angstrom, b = 6.4999(2) angstrom, c = 11.0483(5) angstrom, V = 754.70(7) angstrom(3), and Z = 8. The Fe-57 Mossbauer data collected at different stages of galvanometric cycling confirmed that only 1 mol of alkali metal is extractable between 1.0 V and 5.1 V vs. Li+/Li with a discharge capacity between 135 and 145 mA h g(-1). Li/Na electrochemical ion exchange occurs during cycling and leads to a lithium rich phase. (c) 2013 Elsevier B.V. All rights reserved.