Silicon (Si)-based materials are considered as potential alternative anode materials to graphite for a use in the lithium-ion batteries for electric vehicles and energy storage systems because of superior theoretical capacity of 3759 mAhg −1 at room temperature 1,2 and appropriate operation voltages of a few hundreds milivolts above lithium. However, the Si is well known to suffer from severe volume change during reaction with lithium 3 followed by electrochemical and mechanical particle disintegration 2,4 leading to a poor cycling ability. Recent reports have shown that the use of amorphous 5 or nanostructured Si, 6 and carboncoating 7,8 or carbon composite, 9-11 and the use of advanced elastic binder 12-14 and electrolyte composition 15,16 yields enhancement of cycling ability. It still however remains a great challenge to develop new approaches for obtaining a reliable performance of lithium-ion batteries employing Si-based anodes.Our earlier work showed that the interfacial reaction between LiPF 6 of commercial electrolyte and the Li x Si deleteriously affects cycling performance.17-20 The interfacial reaction did not provide the formation of a stable solid electrolyte interphase (SEI) layer at the Si surface but deactivates the Si gradually with cycling by surface coverage with PF-containing species together with LiF salt, while accelerating irreversible particle disintegration and a consequent and dynamic change in the active surface area. We have proposed that interfacial control is a promising approach for improving the cycling ability of Si-based anodes, which was determined based on a basic understanding of electrode-electrolyte interfacial reactions and its impacts on structural degradation and performance fade via electrochemical and interfacial studies of film model electrodes. Surface protection of Si was necessary both to prevent the attack by LiPF 6 -derived species and to form a stable SEI layer. 17-20In the present work, we demonstrate that the cycling ability of Si nanoparticle anode is improved via a new approach of interfacial control. In order to suppress direct interfacial contact between Si and electrolyte while protecting the Si surface, we build up siloxane network as an artificial SEI at the surface of bulk Si active material, utilizing self-organized condensation reaction between alkoxy groups of silane molecules and hydroixde or oxygen groups of Si surface. The Si nanoparticles and composite with graphite decorated with an artificial SEI show significantly improved cycling stability.Building up of an artificial SEI with siloxane network is simply made first by dispersing commercial Si nanoparticles in the solution of tris(2-methoxyethoxy)vinylsilane (hereafter TMVS) using ultrasonication. The presence of a trace of water in the electrolyte assists the hydrolysis and polycondensation of silanes forming the siloxane network at the Si surface.

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