1 research outputs found
Ab Initio Structure Search and in Situ <sup>7</sup>Li NMR Studies of Discharge Products in the Li–S Battery System
The
high theoretical gravimetric capacity of the Li–S battery
system makes it an attractive candidate for numerous energy storage
applications. In practice, cell performance is plagued by low practical
capacity and poor cycling. In an effort to explore the mechanism of
the discharge with the goal of better understanding performance, we
examine the Li–S phase diagram using computational techniques
and complement this with an in situ <sup>7</sup>Li NMR study of the
cell during discharge. Both the computational and experimental studies
are consistent with the suggestion that the only solid product formed
in the cell is Li<sub>2</sub>S, formed soon after cell discharge is
initiated. In situ NMR spectroscopy also allows the direct observation
of soluble Li<sup>+</sup>-species during cell discharge; species that
are known to be highly detrimental to capacity retention. We suggest
that during the first discharge plateau, S is reduced to soluble polysulfide
species concurrently with the formation of a solid component (Li<sub>2</sub>S) which forms near the beginning of the first plateau, in
the cell configuration studied here. The NMR data suggest that the
second plateau is defined by the reduction of the residual soluble
species to solid product (Li<sub>2</sub>S). A ternary diagram is presented
to rationalize the phases observed with NMR during the discharge pathway
and provide thermodynamic underpinnings for the shape of the discharge
profile as a function of cell composition