Journal
SMALL
Volume 17, Issue 30, Pages -Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/smll.202100146
Keywords
cathode materials; honeycomb ordering; P2; O3 biphasic structure; sodium ion batteries; transition metal oxide
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Funding
- National Research Foundation of Korea (NRF) - Korea government (MSIP) [2020R1A2B5B02002247, NRF-2020M3H4A1A03084258]
- R&D convergence program of the National Research Council of Science Technology [CAP-15-02-KBSI]
- School of Chemistry at The University of New South Wales (UNSW)
- Faculty of Sciences at The University of New South Wales (UNSW)
- National Research Council of Science & Technology (NST), Republic of Korea [C140110] Funding Source: Korea Institute of Science & Technology Information (KISTI), National Science & Technology Information Service (NTIS)
- National Research Foundation of Korea [2020R1A2B5B02002247] Funding Source: Korea Institute of Science & Technology Information (KISTI), National Science & Technology Information Service (NTIS)
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This study presents a lithium-substituted Fe/Mn-based P2/O3 layered oxide that overcomes structural instability and effectively constrains undesirable phase transitions through honeycomb ordering. The results highlight the correlation between the P2/O3 biphasic structure and electrochemical performance.
Layered transition metal oxides, in particular P2-type ones, are considered as promising cathode materials for sodium-ion batteries on account of their high specific capacity and rate capability. Nevertheless, conventional layered compounds involve detrimental phase transformation throughout repeated cycles, which results in electrochemical performance degradation. Therefore, finding structurally stable layered compounds, featuring minimal phase transition has been a key theme of the sodium-ion battery research. Here lithium substituted Fe/Mn-based P2/O3 layered oxide-Na0.67Li0.2Fe0.2Mn0.6O2-that overcomes the inherited structural instability, is reported. In situ synchrotron-based diffraction measurements and DFT calculations are utilized, in order to identify the association between P2/O3 biphasic structure and electrochemical performances. The lithium honeycomb ordering within the P2/O3 biphasic layered compound effectively constrains the undesirable phase transitions; more specifically, both P2-Z phase transition and Jahn-Teller distortion are suppressed throughout wide potential range of 1.5-4.5 V. The DFT calculation further discovers that the presence of honeycomb ordering is crucial for achieving the structural stability by forming Na-vac-Li and Na-Li-Na pairing at highly charged state. The results highlight that the synergetic effect of P2/O3 biphasic structure and lithium substitution can provide an effective strategy toward achieving electrochemically stable layered cathode material for sodium-ion batteries.
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