Journal
CHEMISTRY OF MATERIALS
Volume 33, Issue 13, Pages 4890-4906Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.chemmater.1c00248
Keywords
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Funding
- Engineering Physical Sciences Research Council (EPSRC) via the National Productivity Interest Fund (NPIF) 2018
- EPSRC [EP/L000202]
- Center for Functional Nanomaterials, Brookhaven National Laboratory, through the U.S. Department of Energy, Office of Basic Energy Sciences [DE-AC02-98CH10866]
- US Department of Energy, Office of Basic Energy Sciences [DE-SC0012583]
- EPSRC Centre for Doctoral Training (CDT) in Nanoscience and Nanotechnology Award [EP/L015978/1]
- National Research Foundation of Korea (NRF) - Korean government (MEST) [2019R1A6A1A10073437]
- U.S. Department of Energy (DOE) [DE-SC0012583] Funding Source: U.S. Department of Energy (DOE)
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This study reports the structural changes in P2-Na-0.67[Mg0.28Mn0.72]O-2, including the formation of a high-voltage Z phase and intergrowth of OP4 and O2 phases. The research shows that reversible Mg2+ migration in the Z phase is favorable at high voltages and is a significant contributor to observed voltage hysteresis.
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-Na-0.67[Mg0.28Mn0.72]O-2. Using ex situ X-ray diffraction, Mn K-edge extended X-ray absorption fine structure, and Na-23 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 Na-0.67[Mg0.28Mn0.72]O-2 and identify qualitative changes in the Na+ ion mobility.
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