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.


\begin{align}
\ce{F2 + 2e^- &<=> 2F^-} &\quad E^\circ &= \pu{+2.87 V} \tag{R1} \\
\ce{Sr &<=> Sr^+ + e^-} &\quad E^\circ &= \pu{-4.10 V} \tag{R2}
\end{align}


In theory, a strontium–fluorine battery would have a voltage of $\pu{6.97 V},$ 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 $\pu{-2.899 V}$ for the stable dication to give a cell potential of $\pu{5.769 V}$. From the CRC Handbook [1], lithium has the lowest element to stable ion potential of $\pu{-3.0401 V},$ which is why it is common in batteries.


### Reference


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


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[gsurfer04 is right that it wouldn't be strontium](https://chemistry.stackexchange.com/a/48785/). If you're going really outlandish and willing to use explosive compounds, then the highest possible cell voltage would be obtained with the following redox reactions, using nitrogen to azide as the anode and krypton difluoride as the cathode:


\begin{align}
&\text{Anode:} &\quad \ce{3 N2 + 2 H+ + 2 e- &<=> 2 HN3} &\quad &\pu{-3.09 V} \tag{R1}\\
&\text{Cathode:} &\quad \ce{KrF2 + 2e- &<=> Kr + 2 F-} &\quad &\pu{+3.50 V} \tag{R2}
\end{align}


This would give $\pu{6.59 V}.$


More practical is to use lithium for the anode which is nearly as good at $\pu{-3.04 V}$ for $\pu{6.54 V}$ total. Hirashige et al. [[1](https://doi.org/10.1016/S0022-1139(00)00332-8)] tried using a $\ce{Li}-\ce{XeF2}$ cell (theoretically $\ce{6.49 V}),$ however they only managed $\pu{4.2 V}.$


### Reference


1. Hirashige, T.; Hagiwara, R.; Ito, Y. Chemical Stability and Electrochemical Activity of Xenon Difluoride in Propylene Carbonate. *Journal of Fluorine Chemistry* **2000**, 106 (2), 205–209. DOI: [10.1016/S0022-1139(00)00332-8](https://doi.org/10.1016/S0022-1139(00)00332-8).


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