  Embedding silicon nanoparticles in an intermetallic matrix is a promising
strategy to produce remarkable bulk anode materials for lithium-ion (Li-ion)
batteries with low potential, high electrochemical capacity and good cycling
stability. These composite materials can be synthetized at a large scale using
mechanical milling. However, for Si-Ni3Sn4 composites, milling also induces a
chemical reaction between the two components leading to the formation of free
Sn and NiSi2, which is detrimental to the performance of the electrode. To
prevent this reaction, a modification of the surface chemistry of the silicon
has been undertaken. Si nanoparticles coated with a surface layer of either
carbon or oxide were used instead of pure silicon. The influence of the coating
on the composition, (micro)structure and electrochemical properties of
Si-Ni3Sn4 composites is studied and compared with that of pure Si. Si coating
strongly reduces the reaction between Si and Ni3Sn4 during milling. Moreover,
contrary to pure silicon, Si-coated composites have a plate-like mor-phology in
which the surface-modified silicon particles are surrounded by a
nanostructured, Ni3Sn4-based matrix leading to smooth potential profiles during
electrochemical cycling. The chemical homogeneity of the matrix is more uniform
for carbon-coated than for oxygen-coated silicon. As a consequence, different
electrochemical behaviors are obtained depending on the surface chemistry, with
better lithiation properties for the carbon-covered silicon able to deliver
over 500 mAh/g for at least 400 cycles.
