Abstract
Sodium (Na)-ion conducting polyanionic structures are among the most promising cathode materials to enable more sustainable Na-based battery chemistries to replace current Libased energy storage systems. Materials adopting the alluaudite structure have been found to reversibly intercalate Na, with phosphate and sulfate derivatives exhibiting moderate to high capacities when used as Na-ion cathodes. However, the development of alluaudite cathodes has been hampered by the fact that largely only Fe2+/3+ redox has been observed in this structure. Herein, we show that the Mn2+/3+ redox couple can be activated through compositional tuning of alluaudite compounds. Specifically, vanadate compounds were explored to increase the electrical conductivity as compared to the phosphates and sulfates. Al substitution was also employed to buffer the Jahn-Teller distortions of Mn(III)O6 octahedra, further facilitating electron transfer and redox processes. We report the synthesis of a series of new Na2Mn3-xAlx(VO4)3 alluaudite cathodes and employ synchrotron Xray diffraction, solid-state nuclear magnetic resonance, scanning electron microscopy, density functional theory, X-ray absorption spectroscopy, and magnetometry to characterize the structure, morphology, electronic, and magnetic properties of the as-synthesized materials. Electrochemical Na de(intercalation) in Na2Mn3-xAlx(VO4)3 (x = 0, 0.05, 0.2) was probed through galvanostatic cycling, galvanostatic intermittent titration technique, and ex situ synchrotron X-ray diffraction. While these materials are all redox active, Al substitution results in a more than 2-fold increase in discharge capacity. The successful activation of a higher voltage Mn2+/3+ redox couple opens up a new compositional space for alluaudite-type Na-ion cathodes.
| Original language | English |
|---|---|
| Pages (from-to) | 4088-4103 |
| Number of pages | 16 |
| Journal | Chemistry of Materials |
| Volume | 34 |
| Issue number | 9 |
| DOIs | |
| State | Published - May 10 2022 |
Funding
This work made use of the shared facilities of the UC Santa Barbara MRSEC (DMR 1720256), a member of the Materials Research Facilities Network ( http://www.mrfn.org ), and the computational facilities administered by the Center for Scientific Computing at the CNSI and MRL (an NSF MRSEC; CNS 1725797, DMR 1720256). Use was made of computational facilities purchased with funds from the National Science Foundation (CNS 1725797) and administered by the Center for Scientific Computing (CSC). The CSC is supported by the California NanoSystems Institute and the Materials Research Science and Engineering Center (MRSEC; NSF DMR 1720256) at UC Santa Barbara. Synchrotron diffraction data and X-ray absorption spectroscopy data were collected at beamlines 11-BM and 20-BM, respectively, at the Advanced Photon Source, Argonne National Laboratory, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. V.C.W., E.E.F., J.F., and E.S. were supported by the NSF Graduate Research Fellowship under Grant No. DGE 1650114. J.F. also acknowledges support from the U.S. DOE Office of Graduate Student Research (SCGSR) program administered by the Oak Ridge Institute for Science and Education under Contract No. DE-SC0014664. R.J.C. was supported by an NSF CAREER award under Award No. DMR 2141754. This work was partially supported by the RISE internship program through the MRSEC Program of the National Science Foundation under Award No. DMR 1720256. We gratefully acknowledge Sir A. K. Cheetham for the helpful discussions regarding synthesis and diffraction analysis.