Fig. 3: Battery electrolyte Raman spectral evolution during cycling.

a, Operando Raman spectroscopy performed during the formation cycle for a LiNi_0.8Co_0.1Mn_0.1O₂ (NMC811) - graphite Li-ion pouch cell with an electrolyte comprising LP57 + 2 wt.% VC. The cell was charged galvanostatically to 4.3 V, potentiostatically held at 4.3 V, and then discharged. b, Raman spectral evolution showing a range of Raman modes of battery electrolytes, particularly: (i) PF₆⁻ anion, symmetric stretch (740 cm⁻¹, green dashed line), (ii) EC, skeletal breathing mode (893 cm⁻¹, dotted red line), (iii) VC, -HC = CH- (1628 cm⁻¹, grey dash-dotted line, displayed in inset where the signal was multiplied by 4, relative to that shown in (b)).