Three to tango requires a site-specific substitution: heterotrimetallic molecular precursors for high-voltage rechargeable batteries. Issue 2 (23rd October 2018)

• Record Type: Journal Article
• Authors: Han, Haixiang; Wei, Zheng; Filatov, Alexander S.; Carozza, Jesse C.; Alkan, Melisa; Rogachev, Andrey Yu.; Shevtsov, Andrey; Abakumov, Artem M.; Pak, Chongin; Shatruk, Michael; Chen, Yu-Sheng; Dikarev, Evgeny V.
• Is Part Of: Chemical science. Volume 10:Issue 2(2019)
• Page Start: 524
• Page End: 534
• Publication Date: 2018-10-23
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1039/c8sc03816c
• Languages: English
• ISSNs: 2041-6520

Abstract

Abstract : A site-specific substitution within the heterobimetallic LiMn2 (thd)5 molecule allows for the design of the "true" hetero tri metallic LiMnCo(thd)5 precursor. Abstract : Design of hetero tri metallic molecules, especially those containing at least two different metals with close atomic numbers, radii, and the same coordination number/environment is a challenging task. This quest is greatly facilitated by having a heterobimetallic parent molecule that features multiple metal sites with only some of those displaying substitutional flexibility. Recently, a unique heterobimetallic complex LiMn2 (thd)5 (thd = 2, 2, 6, 6-tetramethyl-3, 5-heptanedionate) has been introduced as a single-source precursor for the preparation of a popular spinel cathode material, LiMn2 O4 . Theoretical calculations convincingly predict that in the above trinuclear molecule only one of the Mn sites is sufficiently flexible to be substituted with another 3d transition metal. Following those predictions, two hetero tri metallic complexes, LiMn2− x Co x (thd)5 ( x = 1 (1a ) and 0.5 (1b )), that represent full and partial substitution, respectively, of Co for Mn in the parent molecule, have been synthesized. X-ray structural elucidation clearly showed that only one transition metal position in the trinuclear molecule contains Co, while the other site remains fully occupied by Mn. A number of techniques have been employed for deciphering the structure and composition of hetero tri metallic compounds. Synchrotron resonant diffraction experiments unambiguously assigned 3d transition metal positions as well as provided a precise "site-specific Mn/Co elemental analysis" in a single crystal, even in an extremely difficult case of severely disordered structure formed by the superposition of two enantiomers. DART mass spectrometry and magnetic measurements clearly confirmed the presence of hetero tri metallic species LiMnCo(thd)5 rather than a statistical mixture of two hetero bi metallic LiMn2 (thd)5 and LiCo2 (thd)5 molecules. Heterometallic precursors1a and1b were found to exhibit a clean decomposition yielding phase-pure LiMnCoO4 and LiMn1.5 Co0.5 O4 spinels, respectively, at the relatively low temperature of 400 °C. The latter oxide represents an important "5 V spinel" cathode material for the lithium ion batteries. Transmission electron microscopy confirmed a homogeneous distribution of transition metals in quaternary oxides obtained by pyrolysis of single-source precursors.