Role of silicon and carbon on the structural and electrochemical properties of Si-Ni3.4Sn4-Al-C anodes for Li-ion batteries

Varying the amounts of silicon and carbon, different composites have been prepared by ball milling of Si, Ni3.4Sn4, Al and C. Silicon and carbon contents are varied from 10 to 30 wt.% Si, and 0 to 20 wt.% C. The microstructural and electrochemical properties of the composites have been investigated by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and electrochemical galvanostatic cycling up to 1000 cycles. Impact of silicon and carbon contents on the phase occurrence, electrochemical capacity and cycle-life are compared and discussed. For C-content comprised between 9 and 13 wt.% and Si-content >= 20 wt.%, Si nanoparticles are embedded in a Ni3.4Sn4-Al-C matrix which is chemically homogeneous at the micrometric scale. For other carbon contents and low Si-amount (10 wt.%), no homogeneous matrix is formed around Si nanoparticles. When homogenous matrix is formed, both Ni3Sn4 and Si participate to the reversible lithiation mechanism, whereas no reaction between Ni3Sn4 and Li is observed for no homogenous matrix. Moreover, best cycle-life performances are obtained when Si nanoparticles are embedded in a homogenous matrix. Composites with carbon in the 913 wt.% range and 20 wt.% silicon lead to the best balance between capacity and life duration upon cycling. This work experimentally demonstrates that embedding Si in an intermetallic/carbon matrix allows to efficiently accommodate Si volume changes on cycling to ensure long cycle-life.