We report on in situ and ex situ concentration measurements in lithium/polymer–electrolyte/lithium cells during cycling. We have used three different methods which give complementary results, in good agreement with theoretical predictions and previous concentration measurements by Raman confocal microspectroscopy. Our methods allow to obtain concentration maps in the electrolyte, in particular, when dendrites are observed: from these measurements, we can correlate the onset of dendritic growth with local concentration gradients.