Effective Electrochemical Charge Storage in the High-Lithium Compound Li 8 ZrO 6

Nam Tran, Brian D. Spindler, Andrey A. Yakovenko, Kamila M. Wiaderek, Karena W. Chapman, Shuping Huang, William H. Smyrl, Donald G. Truhlar, Andreas Stein

Research output: Contribution to journalArticle

Abstract

Li 8 ZrO 6 is a pseudolamellar compound with high lithium content. Even though it is intrinsically a poor conductor and does not contain a transition metal with easily variable oxidation states, a new synthetic approach to preparing it in nanocomposite form with intimate contact to a conductive carbon by mechanical delamination enabled galvanostatic cycling of coin half-cells containing Li 8 ZrO 6 /C as the cathode and Li metal as the anode at 221 mAh/g (which corresponds to extracting 2 Li per formula unit) over at least 140 cycles. With a higher capacity limit, a discharge capacity of 331 mAh/g (which corresponds to extracting 3 Li per formula unit) was maintained over 15-20 cycles. Ex situ and operando X-ray diffraction (XRD) studies of galvanostatically cycled cells showed that at these levels of charge, delithiation follows a reversible, topotactic path with only small distortions around Zr atoms. During this process, crystalline grain sizes decrease continuously, shortening diffusion lengths within grains but increasing the number of grain boundaries and electrode/electrolyte interfaces. Charge storage in Li 8 ZrO 6 appears to involve partial oxidation of oxygen atoms and production of small-polaron holes, as supported by XRD, X-ray photoelectron spectroscopy, and pair-distribution function studies and predicted by quantum mechanical calculations. At higher depths of charge, delithiation results in amorphization of the active electrode material. The charge storage mechanism in Li 8 ZrO 6 is unusual among lithium-ion battery electrode materials and involves a combination of mechanisms that resemble intercalation and conversion reactions. With further refinement, Li 8 ZrO 6 /C based materials open up opportunities to develop new cathode materials for lithium-ion batteries that may improve on currently existing capacity barriers.

Original languageEnglish (US)
Pages (from-to)1274-1287
Number of pages14
JournalACS Applied Energy Materials
Volume2
Issue number2
DOIs
StatePublished - Feb 25 2019

Keywords

  • Li diffusion
  • lithium-ion battery cathode
  • lithium-rich layered oxides
  • octalithium zirconate
  • operando structural characterization

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  • Period 5

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