Haruo Imagawa

Synthesis of a calcium-bridged siloxene by a solid state reaction for optical and electrochemical properties

A Ca-bridged siloxene (Ca-siloxene) resulting from the deintercalation of Ca from CaSi2 was synthesized via a solid state reaction with ethanol wash using TaCl5. The presence of fragmented, two-dimensional siloxene planes with Ca bridging was confirmed. The Ca-siloxene exhibited tunable optical properties, as well as stable Li storage performance by Ca bridging.

Si-based nanocomposites derived from layered CaSi2: influence of synthesis conditions on the composition and anode performance in Li ion batteries

Various Si-based nanocomposites consisting of nanoflake-like CaxSi2 particles and transition metal silicide (MSiy) particles were synthesized by a solid-state exfoliation reaction using layered CaSi2 and transition metal (M) chlorides (M: Ni, Fe or Mn). CaCl2 was found to form in all samples irrespective of the chloride used. Based on the shape and composition of the nanocomposites, it is thought that CaxSi2 particles were formed by extraction of Ca from the layered CaSi2. The molar ratio of CaSi2 and NiCl2 and the synthesis temperature were systematically varied to investigate their influence on the characteristics of the reaction products, e.g. crystalline phases, microstructure, anode capacity as lithium-ion batteries and electrical conductivity. Nanocomposites with various mixtures of CaxSi2 particles (Li storage sites) and NiSiy particles (conducting media) were formed. The synthesized samples showed a wide range of electrical properties depending on the composition. For example, the samples exhibited an anode capacity and an electrical conductivity of 1020 mA h g−1 and 6 × 10−8 S cm−1, or 479 mA h g−1 and 2 × 10−5 S cm−1, respectively. Because of its simplicity, the solid-state exfoliation reaction using layered CaSi2 and MCl2 provides a facile and scalable method to synthesize Si-based nanocomposite anode materials for lithium ion batteries.

Facile and Scalable Synthesis of Silicon-Based Nanocomposites with Slitlike Nanopores: A Solid-State Exfoliation Reaction Using Layered CaSi2

Silicon-based nanocomposites with slitlike nanopores were prepared by heating a mixture of layered CaSi2 and NiCl2. The formation mechanism is based on a solid-state exfoliation reaction wherein the formation of CaCl2 promotes the extraction of Ca from CaSi2, thereby exfoliating the layered structure. The nanocomposites showed anode capacity for lithium ion batteries up to 804 mA h g(-1).