In our study, we correlate the first- and the second-harmonic detection modes of continuous-wave electron paramagnetic resonance (EPR) to identify traces of non-dendritic Li metal present on the graphite anode after multiple electrochemical cycles. Such metallic complexes are a source of limitations which reduce battery life and lead to serious safety issues. To improve their detection, we propose to simultaneously record the first- and second-harmonic EPR spectra.