(Invited) Structural Chemistry of Battery Materials: Metal Oxide Open Frameworks and Li Salts

For several decades, since the discovery of the lithium batteries, the search for novel and improving existing cathode materials and other components of the rechargeable batteries became one of the top priorities of modern technology. In order to develop novel materials, establish structure-property relationship, and find more effective synthetic routes, the knowledge of the crystal structure and comprehensive understanding of the structural changes during battery performance are of the utmost importance. This presentation is based on our more than decade long research on crystallography and structural chemistry of battery materials [1], as well as Li salts and their solvates, conducted in the Institute for Materials Research at Binghamton University. The crystal structure of several dozens of novel compounds has been determined from the powder and single crystal diffraction data. The obtained structural information was used: to analyze the relationship between different structure types for vanadium oxide open frameworks [2]; to establish structural changes or the phase transition during the intercalation and deintercalation processes for an electrochemical cell in Li-VOPO 4 systems [3]; to study the role of pH in the synthesis of the vanadium oxide frameworks and their structure types [4,5]; and to link the red-ox properties with the coordination of the transition metal [2]. Theoretical crystal-chemical analysis of open framework structures allowed us not only to understand known structures and establish a relationship between them but also to deduct and predict new structures. For example, it was possible to deduct 4 possible types of V 3 O 7 layers, only 2 of which were known ( tma V 3 O 7 [4] and [ en 2 Ni]V 6 O 14 [6], tma – tetramethylammonium, en – ethylenediamine), and to predict ordered version (V 5 O 11 ) of disordered “VO 2 ” layer discovered in Li x V 1-y O 2-y .nH 2 O (y = ~1/6) compound [7]. When new lithium bis -oxalatoborate (BOB) salt Li[(C 2 O 4 )B(C 2 O 4 )] was considered for use in the batteries, we have determined its crystal structure from powder diffraction data along with structure of sodium and potassium BOB salts that was quite challenging due to pseudo-hexagonal LiBOB lattice [8]. Recrystallization of LiBOB from the solvent used in the electrochemical cell resulted in solvates with water, acetonitrile, acetone, dimethoxyethylene, 1,3-dioxolane, ethylenecarbonate which crystal structures were determined and are discussed in [9]. Recently the crystal structure determination was successfully performed for several important Li salts: lithium ethylene mono-carbonate (EMC), lithium methyl carbonate (MC) [10], and lithium acetylacetone oxalate borate Li[(acac)B(C 2 O 4 )] [11]. Interestingly LiEMC structure resulted from the compound that was for quite a while claimed to be Li salt with ethylene dicarbonate (EDC). M.S. Whittingham, Solid State Ionics , 134(1-2) , 169-178 (2000); M.S. Whittingham, Chemical reviews , 104(10), 4271-4302 (2004). P.Y. Zavalij and M.S. Whittingham, Acta Cryst ., B55 , 627-663 (1999). Y. Song, P.Y. Zavalij, and M.S. Whittingham, J. Electrochem. Soc. , 152 , A721-A728 (2005). T.G. Chirayil, E.A. Boylan, M. Mamak, P.Y. Zavalij, and M.S. Whittingham, Chem. Comm ., 33-34 (1997). T. Chirayil, P.Y. Zavalij, and M.S. Whittingham, Chem. Mater ., 10 , 2629-2640 (1998). P.Y. Zavalij, F. Zhang, and M.S. Whittingham, Acta Cryst. , B55 , 953-962 (1999). T. Chirayil, P. Zavalij, and M.S. Whittingham, Solid State Ionics , 84 , 163-168 (1996). P.Y. Zavalij, S. Yang, and M.S. Whittingham, Acta Cryst ., B59 , 753–759 (2003). P.Y. Zavalij, S. Yang, and M.S. Whittingham, Acta Cryst ., B60 , 716-724 (2004). L. Wang, A. Menakath, F. Han, Y. Wang, P.Y. Zavalij, D. Iuga, S.P. Brown, C. Wang, K. Xu, and B.W. Eichhorn, Nature Chem ., 11(9) , 789-796 (2019). P.Y. Zavalij, L. Wang, and B.W. Eichhorn , CCDC (2019), doi: 10.5517/ccdc.csd.cc22h53w.