Si nanocrystallites embedded in hard TiFeSi₂ matrix as an anode material for Li-ion batteries

A Si-TiFeSi₂ composite was synthesized in large-scale using arc melting followed by rapid quenching. The composite showed that active Si nanocrystallites of approximately 50 nm were embedded in an inactive TiFeSi ₂ hard matrix. Crystalline Si reacted with Li to form the Li ₂₁Si₈ phase and transformed into amorphous Si when Li was extracted, while the TiFeSi₂ matrix remained inactive to Li and unchanged throughout the electrochemical cycling. The composite showed a reversible capacity of 1200 mAh g^-1 over 50 cycles with a Coulombic efficiency of 89% for the first cycle. Nanosized cracks were observed only at the Si crystallites parts within the Si-TiFeSi₂ particles, indicating that the TiFeSi₂ matrix was hard enough to withstand the stress generated during lithiation which explained the excellent capacity retention.