Nickel‐Molybdenum Sulfide Ni2Mo6 S 7.9 as the Cathode of Lithium Secondary Batteries

Abstract

Nickel-molybdenum sulfide Ni2Mo~Sv.9 (nickel Chevrel phase, NiCP) was tested as the cathode of lithium secondary batteries. The Li/NiCP cell could be galvanostatically discharged up to x = 4 -5 (LixNi2Mo6ST.9) when the current density was smaller than 0.5 mA/cm 2. No evidence of nickel delbosition from the NiCP cathode was observed even after the cell was deeply discharged to x = 4. This resulted in the small distortion of the NiCP crystal lattice upon lithium intercalation, which was clearly observed by the experimental result that the ar value of the rhombohedral lattice parameter hardly changed before and after lithium intercalation. As a result, the NiCP cathodes showed excellent discharge-charge cycling properties. In a deep cycling test carried out between 1.5-2.7V, more than 50% of the initial discharge capacity was maintained even after 200 cycles. In shallow range cycling tests performed in the ranges of 0.5 < x < 1 and 1 < x < 2, the cells were cycled more than 5000 and 1700 times, respectively.Volumetric energy density of a battery (Wh/liter) sometimes becomes more important than gravimetric energy density (Wh/kg), especially when the cell volume is strictly limited as in the case of small-size portable batteries. Ternary molybdenum sulfides M,Mo6Ss-z (M = metal), socalled Chevrel phase compounds (1), are one of the most promising candidates for such high volumetric energy density cells because of their high specific densities: e.g.,

Nonaqueous magnesium electrochemistry and its application in secondary batteries

“…The arrangement of these tetrahedral sites can be configured in channels that penetrate the host in three dimensions (Fig. 8b) 53. The Chevrel crystal structure has two important features: 1) Delocalization of guest atoms.…”

“… Crystal structure of the Chevrel phase: ( a ) vacant sites for Mg ++ ions between two Mo 6 S 8 blocks; ( b ) arrangement of the vacant cation sites in the Chevrel host (Ref. 53). …”

Mixed Metal Sulfides for Electrochemical Energy Storage and Conversion

“…Up to now, various synthetic methods have been developed to prepare MMSs. The solid‐state method is used earliest to synthesize MMSs, in which two metals and sulfur are first mixed together and then heated at high temperature under inert atmosphere or vacuum condition . For the solid‐state method, it usually needs high temperature (>500 °C) and long reaction time (usually several days).…”

“…After several charge–discharge cycles, these materials were fully converted to Mo 6 S 8 , which was not stable at room temperature, leading to poor deep cycling behaviors. On the other hand, no metal deposition in the cathodes of Ni x Mo 6 S 8− y , Co x Mo 6 S 8− y , Fe x Mo 6 S 8− y , and Cr x Mo 6 S 8− y even after deep cycling resulted in improved cycling behavior . However, their relatively low specific capacities (below 100 mA h g −1 ) and operating voltages (around 2 V vs Li/Li + ) have hindered their use as cathode materials in commercial cells.…”

Superconducting Chevrel phase PbMo$_{6}$S$_{8}$ from first principles

“…Their peculiar crystal structure, characterized by molecular-like interpenetrating Mo 6 octahedra and X 8 cubes, allows for a wide chemical variability as different chemical species can be intercalated into the structure, a fact which is at the origin of the broad spectrum of interesting physical properties they display. Owing to the peculiar cage-like structure, Chevrel phases have been considered as promising thermoelectric materials [4][5][6][7] , as cathode materials in battery design 8,9 and, when X=S, as catalysts in desulfurization processes [10][11][12] . As superconductors, the importance of Chevrel phases is linked to the extremely high critical magnetic field (H c2 ), up to ≈ 60 Tesla 13 , that combines with critical temperatures (T c ) as high as 15 K. For these figures Chevrels have been considered a valuable alterna-tive to the A15 SC class for the fabrication of SC magnets 14,15 .…”