Electrochemical Characteristics of Ti–P Composites Prepared by Mechanochemical Synthesis

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Abstract
Titanium phosphide composites with various Ti∕PTi∕P molar ratios (1:1, 1:2, and 1:4) were synthesized by a mechanochemical method and their potential use as an alternative anode material for Li secondary batteries was investigated. The titanium phosphide composites with Ti∕PTi∕P molar ratios of 1:1 and 1:2 did not show any electrochemical reactivity with Li, while both the TiP2TiP2 and P in the composite with a Ti∕PTi∕P molar ratio of 1:4 reacted with Li, yielding a reversible capacity of 1422mAh∕g1422mAh∕g . Ex situ X-ray diffraction analyses and X-ray absorption spectroscopy showed that the TiP2–PTiP2–P composite transformed into cubic Li10.5TiP4Li10.5TiP4 phase without decomposing into Ti and Li3PLi3P during the initial Li insertion. Subsequent cycling showed a highly reversible insertion/extraction process of Li to/from Li10.5TiP4Li10.5TiP4 phase, accompanied by the loss/recovery of the long-range cubic order. The cubic Li10.5TiP4Li10.5TiP4 phase showed excellent cycling performance with a large capacity of 625mAh∕g625mAh∕g for 80cycles80cycles when the amount of lithium reacted was suitably controlled.