US Patent 7858232 Non-aqueous electrolyte secondary battery

A non-aqueous electrolyte secondary battery that has a high electrical capacity and exhibits excellent cycle characteristics even when the battery is rapidly charged and discharged at a large current includes: a positive electrode capable of reversibly absorbing and desorbing Li; a negative electrode; and a non-aqueous electrolyte. The negative electrode includes an alloying material that is capable of electrochemically absorbing and desorbing Li, and includes an A phase composed mainly of Si and a B phase including an intermetallic compound of at least one transition metal element and Si. The transition metal element is selected from the group consisting of Ti, Zr, Ni, Cu, and Fe. At least one of the A phase and the B phase includes a microcrystalline or amorphous region. The weight percent of the A phase relative to the total weight of the A phase and the B phase is greater than 40% and not greater than 95%.