Решение в лоб:

@for /f "tokens=2 delims= " %%i in ('date /t') do set CURDATE=%%i
@for /f "tokens=1 delims=/" %%i in ('echo %CURDATE%') do set CURMONTH=%%i
@for /f "tokens=2 delims=/" %%i in ('echo %CURDATE%') do set CURDAY=%%i
@for /f "tokens=3 delims=/" %%i in ('echo %CURDATE%') do set CURYEAR=%%i
set OUTDATE=%CURYEAR%-%CURMONTH%-%CURDAY%
mkdir %OUTDATE%

Более изящное решение, работает правда не везде.

SetLocal EnableDelayedExpansion
set OUTDATE=%date:~6,4%-%date:~3,2%-%date:~0,2%
mkdir %OUTDATE%