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Porous NiSi-Si composite particles having homogeneously distributed intraparticle pores with the size distribution peaked at 200 nm and a porosity of ϳ40% have been synthesized by a novel method, which comprises steps of ballmilling induced reaction to form Ni/NiSi/Si preform particles and subsequent dissolution of unreacted Ni. Upon lithiation/delithiation cycling, the composite particle electrode exhibits much reduced thickness expansion and capacity fading rate, as compared with the pure Si particle electrode. The improvements have been attributed to the success in introducing the preset voids to partially accommodate volume expansion arising from Si lithiation. In situ synchrotron XRD further indicates that NiSi of the composite is active toward Li alloying, and it undergoes reversible transformation to/from Ni 2 Si and Li y Si. The reversible transformation between the silicides involves volume change in opposite to lithiation of Si, and is beneficial to stabilizing the composite electrode upon charge/ discharge cycling.

Lithium-ion batteries operate beyond the thermodynamic stability of the aprotic organic electrolyte used and electrolyte decomposition occurs at both electrodes. The electrolyte must therefore be composed in a way that its decomposition products form a film on the electrodes which stops the decomposition reactions but is still permeable to the Li(+) cations which are the charge carriers. At the graphite anode, this film is commonly referred to as a solid electrolyte interphase (SEI). Aprotic organic compounds containing vinylene groups can form an effective SEI on a graphitic anode. As examples, vinyl acetate (VA) and acrylonitrile (AN) have been investigated by in-situ Fourier transform infrared (FTIR) spectroscopy in a specially developed IR cell. The measurements focus on electrolyte decomposition and the mechanism of SEI formation in the presence of VA and AN. We conclude that cathodic reduction of the vinylene groups (i.e., via reduction of the double bond) in the electrolyte additives is the initiating and thus a most important step of the SEI-formation process, even in an electrolyte which contains only a few percent (i.e. electrolyte additive amounts) of the compound. The possibility of electropolymerization of the vinylene monomers in the battery electrolytes used is critically discussed on the basis of the IR data obtained.

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This paper introduces a novel in situ method for monitoring electrode reactions in lithium-ion batteries parallel to the electrochemical experiment (in situ electrochemical environmental scanning electron microscopy). Alloy and alloy/carbon composite electrodes suffer from large volume changes followed by cracking and loss of electronic contact of the particles. The measurement setup and the cell principle are described. Reactions occurring on the surface of a Sn/carbon/binder composite electrode during the lithiation process are presented for illustration.The new method provides insight into the dynamics of electrode reactions, shape changes of particles, spatial distribution of solid electrolyte interphase reactions, etc.