Is a strontium-fluorine battery the highest voltage battery using pure elements? Strontium has a very low standard electrode potential and fluorine has a very high one.

$$ E_{\ce{F2 + 2e^- -&gt; 2F^-}} = 2.87\mathrm{V} $$
$$ E_{\ce{Sr -&gt; Sr^+ + e^-}} = -4.10\mathrm{V} $$

In theory a strontium-fluorine battery would have a voltage of $6.97\mathrm{V}$ although there are many practical reasons such as danger and rarity of materials for such batteries not to be made.

Is a strontium-fluorine battery the theoretically highest voltage chemical battery using pure elements or is it possible to obtain a higher one?
The half-potential you've given for strontium is only for the first ionisation. The half-potential you'd actually get is -2.899V for the stable dication to give a cell potential of 5.769V. From the CRC Handbook[1], lithium has the lowest element->stable ion potential of -3.0401V, which is why it's common in batteries.

[1]: Lide, David R., ed. (2006). CRC Handbook of Chemistry and Physics (87th ed.). Boca Raton, FL: CRC Press. ISBN 0-8493-0487-3.