Work

Na‐Site Energetics Reconfiguration Enables Full Capacity Utilization of Sodium Iron Sulfate Cathodes

Year: 2026

Type: article

Abstract: ABSTRACT Sodium iron sulfates are promising high‐voltage cathodes for sodium‐ion batteries, but their practical performance is hindered by incomplete utilization of structurally available Na + and sluggish electronic transport. Here, we demonstrate a mixed‐polyanion electrostatic modulation strategy that reconfigures the Na‐site energy landscape of the sulfate‐based framework. This chemical regulation drives a fraction of Na + into the kinetically favorable Na2/Na3 sites to increase Na + accessibility, suppressing occupancy of the Fe–Na‐disorder‐prone Na4 site, and facilitating the subsequent extraction of trapped Na1 sites. Coupled with an electronic percolation network, the resulting cathodes deliver 100 mAh g − 1 at 0.1C in the hard carbon||Na 2.7 Fe 1.7 (SO 4 ) 2.9 (PO 4 ) 0.1 full cell, approaching its theoretical capacity of 102 mAh g − 1 , together with capacity retention of 90% at 5C after 1500 cycles. This work reveals hetero‐anion substitution as a site‐energy reconfiguring strategy for unlocking reversible Na + storage in kinetically constrained polyanion cathodes.

Source: Small

DOI: 10.1002/smll.76436