Synthesis, Structure, and Electrochemical Properties of K-Based Sulfates K₂M₂(SO₄)₃ with M = Fe and Cu

Abstract

Stabilizing new host structures through potassium extraction from K-based polyanionic materials has been proven to be an interesting approach to develop new Li/Na insertion materials. Pursuing the same trend, we here report the feasibility of preparing langbeinite "Fe(SO)" via electrochemical and chemical oxidation of KFe(SO). Additionally, we succeeded in stabilizing a new KCu(SO) phase via a solid-state synthesis approach. This novel compound crystallizes in a complex orthorhombic structure that differs from that of langbeinite as deduced from synchrotron X-ray and neutron powder diffraction. Electrochemically, the performance of this new phase is limited, which we explain in terms of sluggish diffusion kinetics. We further show that KCu(SO) decomposes into KCuO(SO) on heating, and we report for the first time the synthesis of fedotovite KCuO(SO). Finally, the fundamental attractiveness of these S = / systems for physicists is examined by neutron magnetic diffraction, which reveals the absence of a long-range ordering of Cu magnetic moments down to 1.5 K.

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

“…Note that during Li insertion, V 2 (SO 4 ) 3 undergoes a drastic structural rearrangement leading to monoclinic Li 2 V 2 (SO 4 ) 3 , which contains edge‐sharing VO 6 octahedra . Let's recall that also the electrochemical properties of K‐based sulfates with the general composition 2–2‐3 such as K 2 Cu 2 (SO4) 3 and langbeinite‐type K 2 Fe 2 (SO 4 ) 3 were studied, however, only marginal redox activity towards Li was recorded …”

Rechargeable potassium-ion batteries with honeycomb-layered tellurates as high voltage cathodes and fast potassium-ion conductors

“…K-based compounds have also found their niche application in energy storage as host frameworks for reversible reinsertion of Li and Na electrodes. Such compounds include lepidocrocite K 0.8 Li 0.27 Ti 1.73 O 4 14 , K 2 Ti 6 O 13 15 , KFeF 3 16 , K A SO 4 F ( A  = Fe, Co) 17 , KVPO 4 F 18 , fedotovite K 2 Cu 3 O(SO 4 ) 3 19 , K 2 [(VO) 2 (HPO 4 ) 2 (C 2 O 4 )] 20 , KV 3 O 8 21 , K 1.33 Fe 11 O 17 22 , K 2 D 2 (SO 4 ) 3 ( D  = Cu, Fe) 19 , K x V 2 O 5 21 , Prussian analogues 23 , amongst others. Indeed, a great variety of K-based minerals and compounds have been documented, and most have yet to have their electrochemical properties studied.…”

Partial Substitution of Potassium with Sodium in the K2Ti2(PO4)3 Langbeinite‐Type Framework: Synthesis and Crystalline Structure of K1.75Na0.25Ti2(PO4)3

“…Notably, a few Na‐containing langbeinite‐type complex phosphates have been obtained, and the existing examples are limited to Na 2 M III Ti(PO 4 ) 3 (M III =Cr, Fe) . At present, much research effort is being directed to the synthesis of novel battery materials that simultaneously possess the langbeinite‐type structure and light cations . These efforts are based on the following two‐stage approach: 1) to design host structures by using a specific type of cation (e.g.…”

“…Among these materials, the best battery performance was observed for NASICON‐type structures due to their high sodium conductivity and good stability in redox reactions . The composition of polyanionic compounds with the langbeinite‐type structure is very similar to the composition of NASICON‐type ones, and this is why langbeinite‐type compounds are also considered possible new hosts for electrode materials …”

“…[2] The composition of polyanionic compounds with the langbeinite-type structure is very similart ot he composition of NASICON-type ones, and this is why langbeinite-type compounds are also considered possible new hosts for electrode materials. [10] The general compositiono fc ompounds comprising phosphates of alkali and multivalentm etals with NASICON-type structures can be characterizedb yt he following formula: M I x Z 2 (PO 4 ) 3 (M I = Li, Na;Z= aliovalent metal or metals; x = 1.0-4.0). The structurei sb uilt up by at hree-dimensional framework of ZO 6 octahedra and PO 4 tetrahedra sharing all the oxygen vertices;t he [Z 2 (PO 4 ) 3 ]u nit stands out as ac onstitutional block of the framework.W ithin the framework, the alkali metal may occupy two sites:M 1( special position) or M2 (general position that can remain partially or completely vacant).…”