Electrochemical Lithiation Mechanism of Nickel Silicide Electrode

Pure silicide electrodes have attracted attention as a promising anode material in lithium-ion batteries using certain ionic liquid electrolytes. However, the reaction mechanisms of silicide electrodes, particularly the lithiation sites in the crystal lattice and the reaction sites (bulk versus surface), remain unclear. Here, we investigated the electrochemical lithiation mechanism of a nickel silicide (NiSi2) electrode. X-ray diffraction, transmission electron microscopy, and other techniques revealed that NiSi2 phase did not separate and no lithiation of Si generated from NiSi2 occurred. In contrast, 7Li magic angle spinning nuclear magnetic resonance demonstrated that stable deposition–dissolution of Li metal did not occur on the NiSi2 electrode, and electrochemical lithiation of NiSi2 proceeded. Additionally, we investigated the lithiation sites using computational chemistry. The peak positions in the nuclear magnetic resonance spectra differed from those predicted using the calculated valence electron numbers. This resulted from an increase in conduction electrons near the Fermi energy associated with the amount of Li stored in the NiSi2 crystal lattice, followed by a Knight shift.