Sulfate Chemistry for High‐Voltage Insertion Materials: Synthetic, Structural and Electrochemical Insights

Abstract

Rechargeable batteries based on Li and Na ions have been growing leaps and bounds since their inception in the 1970s. They enjoy significant attention from both the fundamental science point of view and practical applications ranging from portable electronics to hybrid vehicles and grid storage. The steady demand for building better batteries calls for discovery, optimisation and implementation of novel positive insertion (cathode) materials. In this quest, chemists have tried to unravel many future cathode materials by taking into consideration their eco‐friendly synthesis, material/process economy, high energy density, safety, easy handling and sustainability. Interestingly, sulfate‐based cathodes offer a good combination of sustainable syntheses and high energy density owing to their high‐voltage operation, stemming from electronegative SO42− units. This review delivers a sneak peak at the recent advances in the discovery and development of sulfate‐containing cathode materials by focusing on their synthesis, crystal structure and electrochemical performance. Several family of cathodes are independently discussed. They are 1) fluorosulfates [AMSO4F], 2) bihydrated fluorosulfates [AMSO4F ⋅ 2H2O], 3) hydroxysulfate [AMSO4OH], 4) bisulfates [A2M(SO4)2], 5) hydrated bisulfates [A2M(SO4)2 ⋅ nH2O], 6) oxysulfates [Fe2(SO4)2O] and 7) polysulfates [A2M2(SO4)3]. A comparative study of these sulfate‐based cathodes has been provided to offer an outlook on the future development of high‐voltage polyanionic cathode materials for next‐generation batteries.

Na2.44Mn1.79(SO4)3: a new member of the alluaudite family of insertion compounds for sodium ion batteries

“…[4][5][6] Using the sulphate-chemistry for Na-based systems, recently Yamada group has reported an alluaudite structured Na 2 Fe 2 (SO 4 ) 3 as a 3.8 V cathode material offering excellent rate kinetics and energy density. This is even more serious in case of polyanionic system having inherently lower theoretical capacity (Q Th ) owing to the weight penalty stemming from spectator ions.…”

Theoretical Analysis of Materials, used in Energy Storage Applications: the Quest for Robust and Accurate Computational Methodologies

“…In the recent years, TM sulfates attracted considerable attention due to the prospect of designing cathode materials with high operating potential and reasonable stability at charge/discharge cycling . The high operating potential of sulfates (e. g. as compared to the oxides with the same TM) is most likely caused by the inductive effect: the polyanionic cations with higher electronegativity tend to have higher energies for electronic redox reactions .…”

Polyanionic Insertion Materials for Sodium‐Ion Batteries

“…[151,152] It led to the unravelling of fluorosulfates, their derivatives and numerous sulfate-based insertion hosts for Li-and Na-ion batteries. [54,153] Following, we are reporting various SO 4 -based polyanionic insertion compounds designed for Na-ion batteries, which can be spotted on the ternary diagram (Figure 9). The structural and electrochemi cal data are summarized in Table 2.…”

“…Nonetheless, these phases are highly hygroscopic with a tendency to form hydrated bisulfates [Na 2 M(SO 4 ) 2 ·nH 2 O, n = 0, 2, 4]. [153] It is tricky to form anhydrous bisulfate directly, but can be derived by controlled dehydration of hydrated bisulfates…”