NaFe3(HPO3)2((H,F)PO2OH)6: A Potential Cathode Material and a Novel Ferrimagnet

K2Fe(C2O4)2: An Oxalate Cathode for Li/Na-Ion Batteries Exhibiting a Combination of Multielectron Cation and Anion Redox

The development of multielectron redox-active cathode materials is a top priority for achieving high energy density with long cycle life in the next-generation secondary battery applications. Triggering anion redox activity is regarded as a promising strategy to enhance the energy density of polyanionic cathodes for Li/Na-ion batteries. Herein, K₂Fe(C₂O₄)₂ is shown to be a promising new cathode material that combines metal redox activity with oxalate anion (C₂O₄ ^2-) redox. This compound reveals specific discharge capacities of 116 and 60 mAh g^-1 for sodium-ion batterie (NIB) and lithium-ion batterie (LIB) cathode applications, respectively, at a rate of 10 mA g^-1, with excellent cycling stability. The experimental results are complemented by density functional theory (DFT) calculations of the average atomic charges.

HPO32- as a building unit for sodium-ion battery cathodes: 3.1 V operation of Na2-xFe(HPO3)2 (0 < x < 1)

We report Na₂Fe(HPO₃)₂ as the first HPO₃^2--based iron(ii) cathode material for sodium-ion batteries, which delivers a reversible capacity of approximately 100 mA h g^-1 at an average reaction voltage of 3.1 V. In situ X-ray diffraction and ex situ⁵⁷Fe Mössbauer spectroscopy clarify reversible (de)sodiation associated with the Fe³⁺/Fe²⁺ redox reaction.

Ax(H3O)2−xMn5(HPO3)6 (A = Li, Na, K and NH4): open-framework manganese(ii) phosphites templated by mixed cationic species

Four new manganese(ii) phosphites templated by alkali metal ions (Li⁺, Na⁺ and K⁺) and ammonium cations were achieved under mild hydrothermal conditions.