Ag3Fe(VO4)2 and AgFeV2O7: Synthesis, Structure, and Electrochemical Characteristics of Two New Silver Iron(III) Vanadates

The structural features and electrochemical properties of two new silver iron(III) vanadates have been determined, and their relevance to cathode materials for primary lithium battery devices is reported. Ag3Fe(VO4)(2) (SFVO-1) and AgFeV2O7 (SFVO-2) were isolated via a pseudoternary (Ag2O-Fe2O3-V2O5) system at 600 degrees C. The crystallographic data of the phases are the following: Ag3Fe(VO4)(2) monoclinic C2/c (no. 15), a = 9.771(2) angstrom, b = 5.153(1) angstrom, c.= 14.325(3) angstrom, beta = 93.8 5(3)degrees, V = 719.7(2) angstrom(3), Z = 4; AgFeV2O7, triclinic, P1 (no. 2), a = 5.603(1) angstrom, b = 7.485(2) angstrom, c = 7.644(2) angstrom, alpha = 65.07(3)degrees, beta = 89.48(3)degrees, gamma = 78.98(3)degrees, V = 284.4(1) angstrom(3), Z = 2. The single crystal X-ray diffraction studies show that the Ag+ cations reside in the open space of layered (SFVO-1) and channeled (SFVO-2) Fe-O-V frameworks. The extended electrochemical capacity above 2 V (vs Li/Li+) in these phases is consistent with their higher (Ag++Fe3+)/V5+ ratios, compared to the corresponding Ag+/V5+ in Ag2V4O11 (SVO). The discharge voltage of SFVO-1 exhibits a short initial plateau at similar to 3.15 V, corresponding to the reduction of 0.5 x [Ag(I) -> Ag(0)], followed by an abrupt drop to similar to 2.3-2.0 V where the remaining silver (2.5 equiv Li) and some of the framework iron (0.8 equiv Li) are reduced. SFVO-2 has a nominal capacity of 293 mA h/g exhibiting several plateaulike features between 2.5 and 2.0 V. SFVO-1,2 represents the first family of silver iron(III) vanadate phases that have been systematically investigated.