I've searched the Google and not been able to find a definite statement, but it seems that Format-Volume is not available in PowerShell on Windows 7. See below for the output of my psversiontable. From what I can tell, I should be able to use Format-Volume in PS4, and yet I can't. Any help is deeply appreciated.
Format-Volume is part of the Storage module introduced, as Don stated, with Windows 8. The storage module is a CDXML module – take a CIM (WMI) class, wrap it in XML and publish as a module – see PowerShell and WMI (https://www.manning.com/books/powershell-and-wmi) for full details.
The CIM classes on which the Storage module is based were introduced with Windows 8. There has been no, and its very unlikely there ever will be an, effort to make those CIM classes available for pre-Windows 8 versions of Windows.
For Windows 7 and earlier use the Format method on the Win32_Volume class to achieve the same effect.