This research proved that neutron depth profiling (NDP) is a useful technique that provides insight into lithium transport within lithium-ion cells. Studies were conducted utilizing NDP to examine lithium-ion cell behavior under three environmental and operational parameters: (i) storage of cells at temperature, (ii) cell charge/discharge cycling, and (iii) charge/discharge rate and state of charge. During the first study, where cells were stored at 50 degrees C for up to 140 days, the solid electrolyte interface growth rate was determined to range up to 4.8 nm per day depending on the cell capacity. The second study involving cell charge/discharge cycling did not reveal a statistically significant buildup of lithium near the cathode-electrolyte surface; however, the depth profiles showed an increased fluctuation in lithium concentrations as the number of cycles increased. Depth profiles from the third area of investigation quantified the linear relationship between lithium buildup near the cathode-electrolyte surface and the rate of charge (ranging from 0.1 to 4 C in this study). (C) 2009 The Electrochemical Society. [DOI:10.1149/1.3216033] All rights reserved.