Article pubs.acs.org/cm
Molybdenum Polysulfide Chalcogels as High-Capacity, Anion-RedoxDriven Electrode Materials for Li-Ion Batteries Vicky V. T. Doan-Nguyen,*,†,‡ Kota S. Subrahmanyam,§ Megan M. Butala,∥ Jeffrey A. Gerbec,⊥ Saiful M. Islam,§ Katherine N. Kanipe,∇ Catrina E. Wilson,∇ Mahalingam Balasubramanian,# Kamila M. Wiaderek,# Olaf J. Borkiewicz,# Karena W. Chapman,# Peter J. Chupas,# Martin Moskovits,∇ Bruce S. Dunn,@ Mercouri G. Kanatzidis,§ and Ram Seshadri‡,∥,∇ †
California NanoSystems Institute, University of California, Santa Barbara, California 93106, United States Materials Research Laboratory, University of California, Santa Barbara, California 93106, United States § Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States ∥ Materials Department, University of California, Santa Barbara, California 93106, United States ⊥ Mitsubishi Chemical Center for Advanced Materials, Santa Barbara, California 93106, United States ∇ Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106, United States # X-ray Science Division, Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, United States @ Department of Materials Science and Engineering, University of California, Los Angeles, California 90095, United States ‡
S Supporting Information *
ABSTRACT: Sulfur cathodes in conversion reaction batteries offer high gravimetric capacity but suffer from parasitic polysulfide shuttling. We demonstrate here that transition metal chalcogels of approximate formula MoS3.4 achieve a high gravimetric capacity close to 600 mAh g−1 (close to 1000 mAh g−1 on a sulfur basis) as electrode materials for lithium-ion batteries. Transition metal chalcogels are amorphous and comprise polysulfide chains connected by inorganic linkers. The linkers appear to act as a “glue” in the electrode to prevent polysulfide shuttling. The Mo chalcogels function as electrodes in carbonate- and ether-based electrolytes, which further provides evidence of polysulfide solubility not being a limiting issue. We employ X-ray spectroscopy and operando pair distribution function techniques to elucidate the structural evolution of the electrode. Raman and X-ray photoelectron spectroscopy track the chemical moieties that arise during the anion-redox-driven processes. We find the redox state of Mo remains unchanged across the electrochemical cycling and, correspondingly, the redox is anion-driven.
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volume changes upon cycling,7 and the polysulfide shuttle involving diffusion of LinSx through the bulk electrolyte.8−13 We have studied the use of amorphous transition metal polysulfides (chalcogels) as the active material in an electrode to overcome the poor kinetics of lithium diffusion and to prevent the polysulfide shuttling that occurs in Li−S batteries. Transition metal nitrides, oxides, fluorides, phosphides, and sulfides have been investigated as alternatives to S electrodes.2 More specifically, transition metal sulfide (Cr,14 Mn,15 Fe,16 Ni,17 and Cu18) and disulfide (Fe,19 Co,20 Ni,21 Mo,22 and W23) systems have been studied because of their high theoretical gravimetric capacities, which have been demonstrated to reach 900−1300 mAh g−1 upon the first discharge.24
INTRODUCTION
Conversion-based lithium-ion (Li-ion) batteries provide a higher gravimetric capacity alternative to intercalation-based mechanisms, which are limited to extraction and insertion of
