Why divalent magnesium is less reactive than monovalent lithium? Intuitively second group elements should have lower ionization energy than first group but we observe opposite. For example magnesium batteries suffer from slow intercalation of magnesium cation into the cathode much more than lithium batteries. Please refer to this publication
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$\begingroup$ Would Chemistry be a better home for this question? $\endgroup$– Qmechanic ♦Commented Sep 17, 2015 at 13:41
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It's precisely because it is divalent that $Mg$ is less reactive than $Li$.
Magnesium has the electron configuration $[Ne]3s^2$. To form the stable cation $Mg^{2+}$ (which has the extremely stable electron configuration of $Ne$) it needs to 'lose' 2 electrons and the second ionisation energy is very high ($+1450.7 \text{ kJ/mol}$, much higher than the first ionisation energy of $Li$ of +$520.2 \text{ kJ/mol}$).
So although the first ionisation energy of $Mg$ is lower than that of $Li$, it's the second ionisation energy of $Mg$ that matters here: $Li^+$ ions are stable but $Mg^+$ ions are not.
Intercalation of cations is not caused by this though.
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$\begingroup$ This was exactly what I was looking for thank you. $\endgroup$ Commented Sep 17, 2015 at 14:35
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