A new lithium salt with a chelate complex of phosphorus for lithium battery electrolytes

A new Li salt, lithium tris[1,2-benzenediolato(2)-O,O'] phosphate, was synthesized and utilized in Li battery electrolytes for Li/V2O5 cells. This Li salt has a hexacoordinated chelate- type phosphorus anion produced from a pentacoordinated organophosphorus compound as a useful intermediate. It is thermally stable due to the chelating effect with the bidentate ligands of the anion which is a feature distinct from the common Li battery salt LiPF6. The thermal decomposition temperature is higher than that of the pentacoordinated intermediate, and the decomposition process is proven to occur in two steps with release of the benzene moiety from the anion. The specific conductivity (3.89 mS cm(-1)) in an ethylene carbonate-tetrahydrofuran binary mixture (mole fraction of tetrahydrofuran is 0.7) is somewhat low, which can be explained by their high viscosities based on the large anion size. In spite of the low conductivity, the discharge capacity approaches the theoretical value, and a high energy density (410 Wh kg(-1)) is obtained for a Li/V2O5 cell discharged to a cutoff potential of 2.5 V vs. Li/Li+. (C) 1999 The Electrochemical Society. S1099- 0062( 98) 09- 096- 8. All rights reserved.