BEHAVIOR OF NITROGEN-SUBSTITUTED CARBON (NZC1-Z) IN LI/LI(NZCL1-Z)6 CELLS

Nitrogen-containing carbons NzC1-z have been made from different precursors at temperatures between 850 and 1050-degrees-C. Their composition and structure have been studied by chemical analysis, powder x-ray diffraction, x-ray absorption spectroscopy, and Auger electron spectroscopy. These techniques show that some nitrogen has been incorporated substitutionally for carbon. Nitrogen affects the behavior of Li/Li(NzC1-z)6 electrochemical cells in two ways. First, the irreversible capacity observed during the first electrochemical reaction of Li with NzC1-z (during the first discharge) increases with the nitrogen content of the samples. Second, the incorporated nitrogen causes a shift of the cell capacity to lower voltages compared to pure carbon electrodes. The first effect can be understood qualitatively using a model where Li reacts irreversibly with nitrogen-containing species (we call these nitrogen atoms chemical nitrogen) to form lithium-nitrogen-organic compounds. The second effect is caused by the nitrogen which has been substituted for carbon in the lattice (so-called lattice nitrogen). Such nitrogen-containing carbons are not considered useful as anodes for Li-ion cells.