| abstract |
The present invention provides a negative active material for a secondary battery with an improved expansion rate, which is formed by a formula below, and in which an expansion rate of the negative active material after 50 cycles is 70 to 150%, and an amorphization degree on a matrix within an alloy has a range of 25% or more, and Si has a range of 60 to 70%, Ti has a range of 9 to 14%, Fe has a range of 9 to 14%, and Al has a range larger than 1% and less than 20%. Formula: Si x Ti y Fe z Al u (x, y, z, and u are at %, x: 1−(y+z+u)). |