NiFe Cells at High Temperature

Hi

I know little of electrochemistry. What is to stop a rechargeable NiFe cell operating at above, say, 150C assuming it's sealed and proof against pressure and constructed of suitable materials?

Is there some chemical reason why it wouldn't work? I'm not particularly bothered about self discharge, as long as it can retain most of its charge at temperature for a day or so.

Thanks

-- Keith