字符串转换日期错误

我正在尝试做一个动态表，其中，列数取决于日期范围。因此，我正在尝试使用数据透视表。每次我运行查询时，都会出现以下错误：

Msg 241, Level 16, State 1, Line 18
Conversion failed when converting date and/or time from character string.

这是查询（MSSQL）：

DECLARE @StartDate AS DATETIME  
DECLARE @EndDate AS DATETIME  
DECLARE @Query NVARCHAR(MAX)  
DECLARE @Str_Dates NVARCHAR(MAX)  

SET @StartDate = '2014-05-01'
SET @EndDate = '2014-05-16'

SELECT  @Str_Dates = STUFF(( SELECT DISTINCT
                    '],[' + CONVERT(VARCHAR(10),CreateDate,111)
                    FROM myDB.dbo.SaleTransaction
                    WHERE CreateDate BETWEEN @StartDate AND @EndDate
                    ORDER BY 1 
                    FOR XML PATH('')
                    ), 1, 2, '') 
                    + ']'

SET @Query = 
'SELECT * FROM
(
SELECT CreateDate AS [DATE], ItemID, Description, SUM(Quantity) AS [QTY]
FROM myDB.dbo.SaleTransactionDetails
WHERE CreateDate BETWEEN '+@StartDate+' AND '+@EndDate+'
GROUP BY CreateDate, ItemID, Description
) tpvt     
PIVOT (SUM(tpvt.QDE) FOR tpvt.DATE
IN ('+@Str_Dates+')) AS pvt'

EXECUTE (@Query)  

如果我删除WHERE CreateDate BETWEEN '+@StartDate+' AND '+@EndDate+'查询，运行不会出现问题。因此，我尝试CONVERT以多种方式使用函数将变量转换为日期，但是没有成功。
知道我该怎么做才能使用此变量并且没有该错误吗？