Sulfate‐Based Cathode Materials for Li‐ and Na‐Ion Batteries

Abstract

Electrochemical energy storage via Li-ion batteries has changed modern life drastically and has enabled technologies such as portable electronic devices, electric vehicles and stationary grid storage. However, with the steadfast technological evolution and increasing energy demands, batteries need to be constantly improved to meet the needs of our society. Furthermore, increasing concerns are raised regarding sustainability, availability of raw materials and cost. Therefore, extensive research efforts have been focused on the development of new battery types leading to the emergence of the Na-ion technology and the discovery of a myriad of new materials. In this context, polyanions became a prominent alternative to layered oxides. A large variety of polyanionic frameworks has been studied in the past years including phosphates, silicates and borates, but it was especially sulfates, which attracted a lot of attention due to their elevated operating voltages. The here presented article gives an overview of the exhaustive research on sulfate-based cathode materials for Li- and Na-ion batteries discussing recent findings and future perspectives.

Sodium iron sulfate alluaudite solid solution for Na-ion batteries: moving towards stoichiometric Na2Fe2(SO4)3

“…1 Thanks to the high electronegativity of the sulfate groups, an inductive effect 2 raises the reduction potential of the Fe 3+ /Fe 2+ couple to ~ 3.8 V vs. Na + /Na 0 . This value of potential is the highest reported for the Fe 3+ /Fe 2+ couple 1,3 and is combined with a theoretical specific capacity of ~ 120 mAh/g if x = 0. 4 Unlike most A 2 M 2 (XO 4 ) 3 compounds, which crystallize in a NASICON structure, [5][6][7] NFS displays an alluaudite-type structure (Figure 1) with large channels favoring fast diffusion of sodium ions.…”

“…This value of potential is the highest reported for the Fe 3+ /Fe 2+ couple 1,3 and is combined with a theoretical specific capacity of ~ 120 mAh/g if x = 0. 4 Unlike most A 2 M 2 (XO 4 ) 3 compounds, which crystallize in a NASICON structure, [5][6][7] NFS displays an alluaudite-type structure (Figure 1) with large channels favoring fast diffusion of sodium ions. 1,4,5,[8][9][10][11] It was soon observed that, in practice, a sodium-rich Na 2+2x Fe 2-x (SO 4 ) 3 phase with x ≈ 0.25 was obtained instead of the stoichiometric compound Na 2 Fe 2 (SO 4 ) 3 4,12 .…”

“…4 Unlike most A 2 M 2 (XO 4 ) 3 compounds, which crystallize in a NASICON structure, [5][6][7] NFS displays an alluaudite-type structure (Figure 1) with large channels favoring fast diffusion of sodium ions. 1,4,5,[8][9][10][11] It was soon observed that, in practice, a sodium-rich Na 2+2x Fe 2-x (SO 4 ) 3 phase with x ≈ 0.25 was obtained instead of the stoichiometric compound Na 2 Fe 2 (SO 4 ) 3 4,12 . The existence of a solid solution range stems from the partial occupancy of several sites in the alluaudite structure.…”

“…The existence of a solid solution range stems from the partial occupancy of several sites in the alluaudite structure. Considering the general formula [A(2)A(2)'][A(1)A(1)'A(1)'' 2 ]M(1)M(2) 2 [XO 4 ] 3 proposed by Hatert et al 13 for the alluaudite structure, in NFS ( Figure 1) the octahedral M(2) site is occupied by Fe 2+ and a small percentage of Na + , the octahedral M(1) site is occupied by Na + , and the remaining Na + partially occupy the [4+4]-coordinated distorted A(1) and A(2)' sites. The other A sites are empty.…”

Lithiation of V2O3(SO4)2 – a flexible insertion host

“…[18][19][20][21] Vanadium sulfates are attractive candidate compounds and while the search for new crystal structures and compositions is ongoing, there are existing vanadium sulfates that can be explored. 18,22 V 2 O 3 (SO 4 ) 2 can accept four Li + ions, delivering a theoretical capacity of 313 mA h g À1 . Here, we study the Li + insertion into V 2 O 3 (SO 4 ) 2 using two methods (1) electrochemical lithiation and (2) chemical lithiation using n-butyllithium.…”