On the correlation between structure and ionic transport of lithium phosphorous oxynitride (LiPON) amorphous electrolytes
Résumé
Lithium phosphorous oxynitride (LIPON), having an amorphous structure, was first synthesized at the Oak Ridge National Laboratory in the 1990s. Its development has arisen from the pursuit of solid electrolytes stable against lithium metal (Li) to fabricate micro-batteries employing radiofrequency sputtering. Strictly speaking, LIPON is not thermodynamically stable against Li. However, a passivating solid electrolyte interphase emerging between Li and LIPON comprises decomposition products (Li3N and Li2O) thermodynamically stable against Li. Along with the electrochemical stability, the low electronic (<10-10 Ω-1.cm-1) and moderate ionic (>10-6 Ω-1.cm-1) conductivity have been also refereed as key properties for thin film electrolytes applications. The relationships between sputtering conditions, chemical composition, local structure, and ionic conductivity of LIPON thin films has been intensively explored and reported in literature. Most studies converge on the fact that the ionic conductivity can be enhanced by increasing the nitrogen concentration up to a saturation point. The controversial debated is centered on the resulting structure once nitrogen is incorporated and on its structural role regarding the ionic transport. Herein, we apply a methodology based on impedance spectroscopy analyses to determine the partial contributions of formation and migration enthalpies on the overall activation energy for ion conduction. The evolution of these quantities on nitrogen content is correlate with structural aspects unveiled employing nuclear magnetic resonance.