Backup not creating a new file
Instead of writing your own backup solution, I would suggest you to look at SQL Server Maintenance Solution by Ola Hallengren.

If you want to use sqlcmd then you can do as below:

Save below file as backup.sql

DECLARE 
    @DatabaseName sysname = N'test_kin'
    ,@DatabaseBackupFileName varchar(255);

SET @DatabaseBackupFileName = 
    'C:\test\' + @DatabaseName 
      + REPLACE(CONVERT(char(8), GETDATE(), 103), '/', '_') + '.bak';

BACKUP DATABASE @DatabaseName
TO DISK = @DatabaseBackupFileName with init, stats =10;


Then using sqlcmd you can do as below :

sqlcmd -S ServerName\InstanceName -i C:\YourScriptDir\Backup.sql