Role of silicon and carbon on the structural and electrochemical properties of Si-Ni$_{3.4}$Sn$_4$-Al-C anodes for Li-ion batteries

TL;DR

This study investigates how varying silicon and carbon contents in Si-Ni₃.4Sn₄-Al-C composites affect their microstructure and electrochemical performance, demonstrating that embedding Si in a homogeneous matrix enhances cycle life for Li-ion battery anodes.

Contribution

It provides new insights into the optimal silicon and carbon contents for improved anode performance and demonstrates the benefits of embedding Si in a homogeneous intermetallic/carbon matrix.

Findings

Homogeneous matrix formation occurs at specific Si and C contents.

Embedding Si in a matrix improves cycle life and capacity.

Optimal performance achieved with 20 wt.% Si and 9-13 wt.% C.

Abstract

Varying the amounts of silicon and carbon, different composites have been prepared by ball milling of Si, Ni$_{3.4}$Sn$_4$, 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 Ni$_{3.4}$Sn$_4$-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 Ni$_3$Sn$_4$ and Si participate to the reversible lithiation mechanism, whereas no reaction between Ni$_3$Sn$_4$ and Li is observed for no homogenous matrix. Moreover, best cycle-life performances are obtained when Si nanoparticles are embedded in a homogenous matrix and Si-content is moderate (<= 20 wt.%). Composites with carbon in the 9-13 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.