Behavior of Nitrogen‐Substituted Carbon ( N z C 1 − z ) in Li / Li ( N z C 1 − z ) 6 Cells

Nitrogen‐containing carbons have been made from different precursors at temperatures between 850 and 1050°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 electrochemical cells in two ways. First, the irreversible capacity observed during the first electrochemical reaction of Li with (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.