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KCrS 2 Cathode with Considerable Cyclability and High Rate Performance: The First K + Stoichiometric Layered Compound for Potassium‐Ion Batteries
Author(s) -
Naveen Nirmalesh,
Park Woon Bae,
Singh Satendra Pal,
Han Su Cheol,
Ahn Docheon,
Sohn KeeSun,
Pyo Myoungho
Publication year - 2018
Publication title -
small
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.785
H-Index - 236
eISSN - 1613-6829
pISSN - 1613-6810
DOI - 10.1002/smll.201803495
Subject(s) - stoichiometry , cathode , materials science , anode , redox , ion , potassium , sulfide , diffusion , phase (matter) , graphite , density functional theory , chemical engineering , chemistry , thermodynamics , composite material , electrode , computational chemistry , organic chemistry , physics , engineering , metallurgy
KCrS 2 is presented as a stable and high‐rate layered material that can be used as a cathode in potassium‐ion batteries. As far as it is known, KCrS 2 is the only layered material with stoichiometric amounts of K + , which enables coupling with a graphite anode for full‐cell construction. Cr(III)/Cr(IV) redox in KCrS 2 is also unique, because LiCrS 2 and NaCrS 2 are known to experience S 2− /S 2 2− redox. O3‐KCrS 2 is first charged to P3‐K 0.39 CrS 2 and subsequently discharged to O′3‐K 0.8 CrS 2 , delivering an initial discharge capacity of 71 mAh g −1 . The following charge/discharge (C/D) shows excellent reversibility between O′3‐K 0.8 CrS 2 and P3‐K 0.39 CrS 2 , retaining ≈90% of the initial capacity during 1000 continuous cycles. The rate performance is also noteworthy. A C/D rate increase of 100‐fold (0.05 to 5 C) reduces the reversible capacity only by 39% (71 to 43 mAh g −1 ). The excellent cyclic stability and high rate performance are ascribed to the soft sulfide framework, which can effectively buffer the stress caused by K + deinsertion/insertion. During the transformation between P3‐K 0.39 CrS 2 and O′3‐K 0.8 CrS 2 , the material resides mostly in the P3 phase, which minimizes the abrupt dimension change and allows facile K + diffusion through spacious prismatic sites. Structural analysis and density functional theory calculations firmly support this reasoning.