Can Lithium-Iron-Phosphate or LiFePO4 batteries be stored in cold?
Lithium batteries are powered by chemical reactions (citation needed).  As a rule of thumb, every +10C doubles the reaction rate -- which means that every -10C halves the reaction rate.  Charging a lithium battery is taxing on them as-is, and it is damaging if the electrolyte is operating at 1/64th of its usual performance (20C -&gt; -40C).  The specific behavior is in your manufacturer's data sheet (if one exists), but it's fairly safe to say the batteries would prefer to be about room temperature.
According to https://apps.dtic.mil/dtic/tr/fulltext/u2/a351962.pdf, the freeze point of conventional LiPo electrolyte is about -30C.  You run a very serious risk of internal mechanical damage in the cell below this point.  I would add 10C to this to give myself headroom.
This gives you a storage temperature of -20C to +20C at roughly 50% SoC (~ 3.8v/cell).  In this range, cooler will be better.  But, you cannot use the cells until their internal temperature has hit operating temperature.  This may be several minutes, or even hours, after the exterior of the cells has warmed.
TLDR: your choice is to not live in Hoth, or take your battery inside.