I am thinking of using a buck-boost DC-DC converter to charge a nominal LiPo battery. Besides the care that needs to be taken not to overcharge a LiPo battery, the issue I am having is whether or not a negative voltage (supplied by the buck-boost) is adequate for charging. Do you think if by reversing the battery terminals, the ground terminal will be x amount of voltage lower than the positive terminal and therefore work?

Thanks

 

What limits the charging current?
What detects the charging current dropping as the battery becomes fully charged and disconnects the charging so that over-charging does not occur?
Why are you asking about simple polarity? If it is backwards then the battery will explode and catch on fire.
Why aren't you using a charger IC made to charge a lithium battery properly?

 

You don't want to fool around with LiPo's, use a proper charger circuit. If you don't want to build your own using an existing IC, then buy a board with the charger on it already. For example:

https://www.kr4.us/search.asp?keyword=lipo+charger&search=

 

If by buck-boost you mean The Treacle-Fired Crumpet Toaster then yes, you can do it. I think the circuit to which you refer is an inverting converter, which is commonly called buck-boost, though it is neither buck nor boost, hence my preference for a misnomer that is at least conspicuously inappropriate. I assume your interest in that topology is because your input voltage may be either less or greater in voltage magnitude than what is required to charge the battery.

Properly implemented, it can do accurate voltage regulation. Accurate current limiting is less easy. Be sure not to try to have different "grounds." If you need to isolate the input from the output so you do have can have separate grounds, that can be done by using two windings on the inductor, to produce what is usually called a flyback converter (function is identical except that the inductor is charged with one winding and discharged with another).