You want to make the format/style explicit and don't rely on interpretation based on local settings (which may vary among your clients infrastructure).
DECLARE @Test AS DATETIME
SET @Test = CONVERT(DATETIME, '2011-02-15 00:00:00', 120) -- yyyy-MM-dd hh:mm:ss
SELECT @Test
While there is a plethora of styles, you may want to remember few
Note that the T in the ISO 8601 is actually the letter T and not a variable.