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Electrodes with carbon coatings need to be cycled at low voltage regimes in order to achieve full graphite lithiation. During the lithiation stage amorphous Li-Si phases turn to crystalline phases [1-6], a process that is associated with a large overpotential on delithiation. This approach differs from other practical strategies to improve capacity retention that limit the Si cycling regimes to 1,200?1,500 mAh/g, cycling at higher potentials between different a-LixSi compositions [7]. To use Si to its full potential a deep understanding of the different structural processes that occur, the kinetics of the various transformations and how they correlate with capacity retention is required. In this work we carried out ex-situ 7Li NMR spectroscopy to follow the lithiation and delithiation of slurries prepared with acid and basic buffers. The approach allows us to follow the structural transformations that occur in the 2nd cycle and beyond involving the nano-structured amorphous Si phase. The ability to control the voltage and current carefully enables an understanding of how the charge and discharge processes are observed by NMR. Figure 1 shows the first charge-discharge cycle and its corresponding NMR spectra. The specific capacity at the end of the first lithiation (discharge capacity) is 3950 mAhg−1 and after delithiation (charge capacity) is 3100 mAhg−1. The irreversible capacity is about 850 mAhg−1. From our results, it was possible to identify, for example, the inhomogeneous growth of crystalline Li3.75Si from the amorphous phase, the electrochemical and NMR signatures of the process involving the over-lithiation of c-Li3.75Si that occurs below 50 mV, and the formation of small clusters within the Li3.75Si phase on charge.