Parallel and serial reduction pathways in complex oxide lithium-ion battery anodes

Authors: Kent Griffith (Northwestern University) , Kenneth Poeppelmeier (Northwestern University)
Co-authored by industrial partner: No

Type: Conference Paper
Conference: XAFS2021
Peer Reviewed: No

State: Published (Approved)
Published: July 2021

Abstract: Complex early transition metal oxides have emerged as leading candidates for fast charging lithium- ion battery anode materials. Framework crystal structures with frustrated topologies are good electrode candidates because they may intercalate large quantities of guest ions with minimal structural response. Starting from the empty perovskite (ReO3) framework, shear planes and filled pentagonal columns are examples of motifs that decrease the structural degrees of freedom. As a consequence, many early transition metal oxide shear and bronze structures do not readily undergo the tilts and distortions that lead to phase transitions and/or the clamping of lithium diffusion pathways that occur in a purely corner-shared polyhedral network. In this work, we explore the relationship between composition, crystal structure, and reduction pathway in a variety of mixed transition metal and main group oxides. Operando and ex situ X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) data are collected at Ga K-edge, Nb K-edge, W LI,II,III-edges, Bi LIII-edge, and Ti K-edges to track the evolution of electronic and local atomic structure of the complex oxides during lithium insertion and extraction. Early transition metals in their fully oxidized d0 electronic states (Ti4+, Nb5+, W6+) undergo inversion-breaking local distortions. When these oxides are reduced, such as in lithiation in a lithium-ion battery, their local symmetry increases. The symmetry dependence of XANES makes it uniquely sensitive to this phenomenon, known as the second-order Jahn– Teller effect. In mixed metal oxides, XANES and EXAFS differentiate the redox centers and reveal that the transition metals proceed along parallel reduction pathways while the main group elements react in a stepwise conversion-type mechanism. X-ray absorption spectroscopy is complemented by 6/7Li and 23Na solid- state NMR spectroscopy, synchrotron and neutron diffraction, and DFT to gain a comprehensive picture of the charge storage mechanisms. Prospects for tunability and implications for charge rate and structural stability will be discussed.

Subject Areas: Materials, Energy, Chemistry

Instruments: B18-Core EXAFS

Added On: 09/08/2021 11:43

Discipline Tags:

Energy Storage Energy Physical Chemistry Energy Materials Chemistry Materials Science

Technical Tags:

Spectroscopy X-ray Absorption Spectroscopy (XAS) Extended X-ray Absorption Fine Structure (EXAFS) X-ray Absorption Near Edge Structure (XANES)