In this work, the reversible insertion of sodium ions in TiP2O7 as the anode material in an aqueous battery is demonstrated. Several polymorphs of TiP2O7 are synthesized using a high temperature solid-state route and a low temperature sol gel route. In addition to physical characterization, the materials are electrochemically characterized in an aqueous 1M Na2SO4 electrolyte against Na0.44MnO2 cathode material. While no capacity for sodium ion cycling is reflected in cyclic voltammetry tests of these TiP2O7, all polymorphs exhibited reversible cycling of sodium ions in constant current galvanostatic cycling with potential limitation. To our knowledge, this is the first report of solid-state synthesized TiP2O7 reversibly cycling sodium ions. Specific capacity is found to be positively correlated with both crystallite size and lattice parameter. A full cell rate study with three electrode data in aqueous Na2SO4 electrolyte is presented.
This work is supported by Carnegie Mellon University and Aquion Energy Inc.
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