$AllVolume = Get-WmiObject Win32_Volume |select name ,DriveLetter,FreeSpace,Capacity
foreach($vol in $AllVolume ){
    if ([string]::IsNullOrEmpty( $vol.DriveLetter)){  }
       else{  
					 $l = "{0:N2}" -f ($vol.FreeSpace /$vol.Capacity *100)
  				 "{0}的磁盘空闲率为 {1} %"  -f  $vol.DriveLetter , $l
    }
}