Polymorphism in Li4Zn(PO4)2 and Stabilization of its Structural Disorder to Improve Ionic Conductivity
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posted on 2018-01-25, 00:00 authored by Sujoy Saha, Gwenaëlle Rousse, Ignacio Blazquez Alcover, Matthieu Courty, Daniel Alves Dalla Corte, Jean-Marie TarasconRealization
of the vulnerability of current rechargeable battery
systems drives the research of solid electrolytes. In the search for
a new Li ion conductor, we explored the rich crystal chemistry of
Li4Zn(PO4)2, which presents a low-temperature
monoclinic (α-) and a high-temperature orthorhombic (β-)
polymorph. We solved the crystal structure of the β phase and
found that it has a disordered Li/Zn-sublattice while showing the
largest conductivity; however, it could not be stabilized at room
temperature by quenching. We discovered that the partial substitution
of Zn2+ with Ga3+ in Li4–xZn1–xGax(PO4)2 first leads to
an intermediate β′ phase. Increasing the Ga content to
0.5 mol pfu enables us to stabilize the pure β phase at room
temperature, which exhibits a conductivity by several orders of magnitude
higher than the pristine sample. The crystal structures of the new
β′/β-phases have been solved to elucidate the conduction
mechanism, which confirms the high sensitivity of ionic conductivity
on disorder.
