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Structural origins of voltage hysteresis in the Na-ion cathode P2–Na0.67[Mg0.28Mn0.72]O2: A combined spectroscopic and density functional theory study

DOI: 10.1021/acs.chemmater.1c00248 DOI Help

Authors: Euan N. Bassey (University of Cambridge) , Philip J. Reeves (University of Cambridge) , Michael A. Jones (University of Cambridge) , Jeongjae Lee (University of Cambridge; Seoul National University) , Ieuan D. Seymour (Imperial College London) , Giannantonio Cibin (Diamond Light Source) , Clare P. Grey (University of Cambridge)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Chemistry Of Materials , VOL 68

State: Published (Approved)
Published: June 2021
Diamond Proposal Number(s): 24303

Open Access Open Access

Abstract: P2-layered sodium-ion battery (NIB) cathodes are a promising class of Na-ion electrode materials with high Na+ mobility and relatively high capacities. In this work, we report the structural changes that take place in P2–Na0.67[Mg0.28Mn0.72]O2. Using ex situ X-ray diffraction, Mn K-edge extended X-ray absorption fine structure, and 23Na NMR spectroscopy, we identify the bulk phase changes along the first electrochemical charge–discharge cycle—including the formation of a high-voltage “Z phase”, an intergrowth of the OP4 and O2 phases. Our ab initio transition state searches reveal that reversible Mg2+ migration in the Z phase is both kinetically and thermodynamically favorable at high voltages. We propose that Mg2+ migration is a significant contributor to the observed voltage hysteresis in Na0.67[Mg0.28Mn0.72]O2 and identify qualitative changes in the Na+ ion mobility.

Journal Keywords: Layers; Ions; Diffraction; Transition metals; Phase transitions

Diamond Keywords: Batteries; Sodium-ion

Subject Areas: Materials, Chemistry, Energy

Instruments: B18-Core EXAFS

Added On: 23/06/2021 14:59


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)