Faster Diffusion and Higher Lithium-Ion Intercalation Capacity in Pb-Jarosite than Na-Jarosite

Pb-jarosite, Pb0.5Fe3(SO4)2(OH)6, was investigated for the first time as an intercalation cathode for lithium-ion batteries. Despite having a lower theoretical specific capacity than its Na-jarosite analogue, NaFe3(SO4)2(OH)6, bulk Pb-jarosite displayed higher lithium-ion capacity, especially at higher current rates. The greater lithium storage is attributed to more kinetically facile diffusion of lithium in Pb-jarosite, as evidenced by potentiostatic intermittent titration technique data, indicating an average diffusion coefficient over 10 times larger. Inductively coupled plasma–optical emission spectroscopy and X-ray diffraction (XRD) measurements showed that the substitution of divalent Pb2+ into monovalent Na+ sites led to an increased number of cation vacancies and a more open structure to facilitate lithium diffusion. Ex situ XRD measurements showed that Pb-jarosite is more resilient to the semireversible crystalline-to-amorphous phase transformation that occurs in Na-jarosite over many cycles. These findings demonstrate that multivalent cation substitution in jarosite materials can significantly improve their performance as intercalation cathodes.