High-energy mechanical milling (HEMM) has been used to generate electrochemically active-inactive nanocomposite anodes for Li-ion applications. However, prolonged milling renders the nanocomposites electrochemically inactive. The causes of electrochemical capacity loss after prolonged HEMM have been studied using different analytical and experimental techniques comprising impedance spectroscopy, four-point probe measurements, high resolution transmission electron microscopy (HRTEM), and X-ray diffraction. The electrical resistivity of the Si/TiN nanocomposites remained unaltered within error even after milling for 18 h. An electrochemically inactive electrode of Si/TiN composite obtained after milling Si and TiN for 9 h exhibited a fivefold increase in charge-transfer resistance (R-ct congruent to 580 Omega) in comparison to an electrochemically active electrode (R-ct congruent to 130 Omega) obtained after milling for 6 h based on the impedance analysis. The chemical and thermodynamic stability of the Si/TiN system has been confirmed through HRTEM and high-temperature stability experiments. HRTEM and electron energy loss spectroscopy analyses results reveal that some of the Si is embedded in the Si/TiN nanocomposite obtained after prolonged milling. All these results suggest that embedding of Si leads to the electrochemical inactivity of the nanocomposites obtained from prolonged HEMM. (C) 2005 The Electrochemical Society.