Trends forms on it in many solvents.13 While still

Trends in Figure 14 indicate that while both Li and MV ions
are not expected to undergo conversion in most 1 electron
reduction processes (i.e., 1 mol of Li or 0.5 mol of MV, left
panel), MV conversion is preferred when two electrons are
transferred per TM (i.e., 1 mol of MV, right panel). This does
not necessarily imply that conversion will take place, as many
Li+ intercalation states are metastable, but it does require a
reliance on kinetic stabilization. Additionally, the voltage
difference between intercalation and conversion reactions
(Vint ? Vconv, width of green bars in the left panel of Figure
14) is nominally higher for Li than for MV ions, making Liintercalation
cathodes very tolerant to degradation due to local
polarization, which could potentially drop the actual potential
below Vconv.
While most MV ions are not expected to undergo conversion
reactions in most oxide hosts at low MV content (or 1e?
reduction), local accumulation of MV ions can occur during
intercalation due to poor MV mobility. A significant increase in
local concentration of MV ions (and the number of electrons
transferred locally) can indeed result in local conversion
reactions, given the tendency for most transition metal oxides
to convert at high MV content (Figure 14, right panel). This
analysis points at a key challenge for Mg2+ intercalation in
oxides. Even though its intercalation kinetics is expected to be
much worse than Li+
, its tolerant polarization window upon
discharge is considerably smaller than for Li+ intercalation due
to the very negative formation energy of MgO. To compound
the problem, MgO is considered to have extremely low
mobility for Mg2+ ions.150 While this has never been proven
rigorously, the difficulty in operating Mg metal anodes is
attributed to the ease by which a blocking MgO layer forms on
it in many solvents.13 While still present, the conversion
challenge seems to be less of an