Silicon has been attracting large interest for a high capacity electrode material used in lithium ion batteries (LIBs) to conquer facing energy density limit (1,2). Recently, some LIBs using negative electrode composed of Si (or SiOx) and carbon are put in market though their cell lives are not excellent. Some of the issues causing the life shortage may come from the rate ununiformity due to their storage structure difference (Li intercalation in carbon and Li-Si alloying in silicon). An Al-laminated half-cell composed of lithium counter electrode and working electrode composed of 20 wt% of Silicon and 80 wt% of graphite for in situ ⁷Li nuclear magnetic resonance (NMR) measurement were fabricated (3,4). The NMR spectra were measured every 10% of SOC (state of charge) during charge (Li insertion) and every 10% of DOD (depth of discharge) during discharge (Li extraction). Peak attributed to Li-Si alloy appeared at 8 ppm from SOC 20% and shifted to higher magnetic field associated with SOC increase and reached -13 ppm at SOC 100%. The peak shifted reversibly to lower field during discharge (Fig. 2). The peak grew with charge SOC increase and reversibly shrunk with discharge DOD. The relaxation change after stooping the charge and discharge is investigating. X-ray diffraction (XRD) of charged electrode sample and electrochemical impedance spectroscopy (EIS) are also examined.