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

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. 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.

Ni–Sn intermetallics as an efficient buffering matrix of Si anodes in Li-ion batteries

“…In this context, our group has developed in the recent years composite materials formed by Si nanoparticles embedded in a buffering matrix containing the intermetallic compound Ni3Sn4, Al and C 25,38,39 . Carbon acts as a process control agent (PCA) during mechanochemical synthesis of the composite by limiting the chemical reaction between Si and Ni3Sn4.…”

Impact of Surface Chemistry of Silicon Nanoparticles on the Structural and Electrochemical Properties of Si/Ni3.4Sn4 Composite Anode for Li-Ion Batteries

“…The composite Si R -NiSn consists of micrometric-size round-shaped particles ( Figure 3 a). The composite particles contain phase domains of dark tonality attributed to silicon nanoparticles [ 30 ] embedded in a light-grey matrix which is chemically homogeneous at the spatial resolution (~50 nm) of the BSE analysis ( Figure 3 b). In the case of material ground with Si C , SEM-SE analysis ( Figure 3 c) shows that the composite particles are in the form of micrometer-sized platelets.…”

“…These three Si-precursors were used to synthetize the composites (Si-Ni 3.4 Sn 4 -Al) via ball milling of Si, Ni 3.4 Sn 4 (99.9%, ≤125 μm, home-made) and Al (99%, ≤75 μm, Sigma-Aldrich, Saint-Louis, USA) powders for 20 h under an inert atmosphere. Further details on intermetallic Ni 3.4 Sn 4 and composite synthesis can be found in [ 30 , 31 , 32 ]. No addition of carbon graphite in the milling jar as PCA was used for the current investigation.…”

“…Following this concept, our group thoroughly investigated composites of general formulation Si-Ni 3.4 Sn 4 -Al-C prepared via mechanochemistry [ 30 , 31 , 32 ]. They consist of submicronic silicon particles embedded in a nanostructured matrix made of Ni 3.4 Sn 4 , aluminum and graphite carbon.…”

“…As reported by [ 33 ], low aluminum content (~3 wt.%) improves the cycle life of Si-Sn-type anodes. Carbon addition acts as a Process Control Agent (PCA), minimizing reactivity between Si and Ni 3.4 Sn 4 on milling [ 30 ]. These composites take advantage of the high capacities of silicon and tin, the good ionic and electronic conductivity of the matrix and its elastic properties to manage volume expansion.…”