NONAQUEOUS ELECTROLYTE SECONDARY BATTERY AND NEGATIVE ELECTRODE THEREOF

摘要

A negative electrode yields a high-performance nonaqueous electrolyte secondary battery which has a high discharging capacity, high charging/discharging efficiency in the initial stage and during cyclic operation, and excellent properties in cyclic operation, and the electrode of which less expands after cyclic operation. The negative electrode includes an active material thin film which mainly contains a compound represented by a general formula SiZ x M y , wherein Z, M, "x" and "y" satisfy the following conditions, of a phase including an element Z lying in a nonequilibrium state in silicon. The element Z is at least one element selected from the group consisting of boron, carbon, and nitrogen. The element M is other than silicon and the element Z and is at least one element selected from the elements of Groups 2, 4, 8, 9, 10, 11, 13, 14, 15, and 16 of the Periodic Table of Elements. The number "x" is such a value'that a Z-concentration ratio Q(Z) falls within the range of 0.10 to 0.95. The Z-concentration ratio Q(Z) is calculated with respect to the Z-concentration (p/(a+p)) of a compound Si a Z p having a composition closest to silicon and being present in equilibrium, wherein "a" and "p" are integers according to the following equation: Q(Z) = [x/(1+x)]/[p/(a+p)]. The number "y" is 0 or more and 0.50 or less.