Considering the alkali metals, Lithium has the highest hydration enthalpy but the most negative electrode potential, why is it this way?

Dear Student,

Lithium has the most negative electrode potential due to its highest hydration enthalpy which owes to its small size. 
Electrode potential represents the overall change
$\mathrm{M}\left(\mathrm{s}\right) \to {\mathrm{M}}^{+}\left(\mathrm{aq}\right)$
It involves three parameters :

1. Sublimation enthalpy for the change $\mathrm{M}\left(\mathrm{s}\right) \to \mathrm{M}\left(\mathrm{g}\right)$
2. Ionisation enthalpy for $\mathrm{M}\left(\mathrm{g}\right)\hspace{0.17em}\to {\mathrm{M}}^{+}\left(\mathrm{g}\right)$
3. Hydration enthalpy for ${\mathrm{M}}^{+}\left(\mathrm{g}\right) \to {\mathrm{M}}^{+}\left(\mathrm{aq}\right)$

Lithium being the smallest ion, has the highest hydration enthalpy which accounts for high negative value of electrode potential.