2 research outputs found
New Mechanistic Insights on Na-Ion Storage in Nongraphitizable Carbon
Nongraphitizable carbon, also known
as hard carbon, is considered one of the most promising anodes for
the emerging Na-ion batteries. The current mechanistic understanding
of Na-ion storage in hard carbon is based on the “card-house”
model first raised in the early 2000s. This model describes that Na-ion
insertion occurs first through intercalation between graphene sheets
in turbostratic nanodomains, followed by Na filling of the pores in
the carbon structure. We tried to test this model by tuning the sizes
of turbostratic nanodomains but revealed a correlation between the
structural defects and Na-ion storage. Based on our experimental data,
we propose an alternative perspective for sodiation of hard carbon
that consists of Na-ion storage at defect sites, by intercalation
and last via pore-filling
High Capacity of Hard Carbon Anode in Na-Ion Batteries Unlocked by PO<sub><i>x</i></sub> Doping
The
capacity of hard carbon anodes in Na-ion batteries rarely reaches
values beyond 300 mAh/g. We report that doping PO<sub><i>x</i></sub> into local structures of hard carbon increases its reversible
capacity from 283 to 359 mAh/g. We confirm that the doped PO<sub><i>x</i></sub> is redox inactive by X-ray adsorption near edge
structure measurements, thus not contributing to the higher capacity.
We observe two significant changes of hard carbon’s local structures
caused by doping. First, the (002) <i>d</i>-spacing inside
the turbostratic nanodomains is increased, revealed by both laboratory
and synchrotron X-ray diffraction. Second, doping turns turbostratic
nanodomains more defective along <i>ab</i> planes, indicated
by neutron total scattering and the associated pair distribution function
studies. The local structural changes of hard carbon are correlated
to the higher capacity, where both the plateau and slope regions in
the potential profiles are enhanced. Our study demonstrates that Na-ion
storage in hard carbon heavily depends on carbon local structures,
where such structures, despite being disordered, can be tuned toward
unusually high capacities