Figure 1.

Schematic of the ⁷Li in situ NMR technique used to study dead Li formation and the resulting ⁷Li NMR spectra. (a) The Cu-LiFePO₄(LFP) cell before cycling and the corresponding ⁷Li NMR spectrum showing the resonance of the diamagnetic Li (the SEI and Li⁺ ions) and the absence of the Li metal peak. (b) Charging the cell results in Li deposition, as shown in the ⁷Li NMR spectrum of the Li metal region. (c) At the end of discharge, the Li metal signal can still be observed, which is attributed to dead Li. (d) Further cycling of the Cu−LFP cell results in an accumulation of dead Li over the next cycles (cycle 2–5), the intensity of the Li metal signal increasing at the end of stripping in each cycle.