Determining Factors in Triggering Hysteretic Oxygen Capacities in Lithium-Excess Sodium Layered Oxides

Sangeon Park; Jaewoon Lee; Hyungjun Kim; Gwanghyeon Chioi; Sojung Koo; Jinwoo Lee; Maenghyo Cho; Duho Kim

doi:10.1021/acsami.2c02438

Determining Factors in Triggering Hysteretic Oxygen Capacities in Lithium-Excess Sodium Layered Oxides

ACS Appl Mater Interfaces. 2022 May 4;14(17):19515-19523. doi: 10.1021/acsami.2c02438. Epub 2022 Apr 22.

Authors

Sangeon Park¹, Jaewoon Lee¹, Hyungjun Kim², Gwanghyeon Chioi¹, Sojung Koo¹, Jinwoo Lee¹, Maenghyo Cho², Duho Kim¹

Affiliations

¹ Department of Mechanical Engineering (Integrated Engineering Program), Kyung Hee University, 1732, Deogyeong-daero, Giheung-gu, Yongin-si, Gyeonggi-do 17104, Republic of Korea.
² Department of Mechanical and Aerospace Engineering & Department of Mechanical Engineering, Seoul National University, 1 Gwanak-ro. Gwanak-gu, Seoul 08826, Republic of Korea.

PMID: 35452216
DOI: 10.1021/acsami.2c02438

Abstract

Oxygen redox (OR) reactions in sodium layered oxide cathodes have been studied intensively to harness their full potential in achieving high energy density for sodium-ion batteries (SIBs). However, OR triggers a large hysteretic voltage during discharge after the first charge process for OR-based oxides, and its intrinsic origin is unclear. Therefore, in this study, an in-depth reinvestigation on the fundamentals of the reaction mechanism in Na[Li_1/3Mn_2/3]O₂ with a Mn/Li ratio (R) of 2 was performed to determine the factors that polarize the OR activity and to provide design rules leading to nonhysteretic oxygen capacity using first-principles calculations. Based on thermodynamic energies, the O^2-/O₂^2- and O^2-/O^n- conditions reveal the monophasic (0.0 ≤ x ≤ 4/6) and biphasic (4/6 ≤ x ≤ 1.0) reactions in Na_1-x[Li_2/6Mn_4/6]O₂, but each stability at x = 5/6 is observed differently. The O-O bond population elucidates that the formation of an interlayer O-O dimer is a critical factor in triggering hysteretic oxygen capacity, whereas that in a mixed layer provides nonhysteretic oxygen capacity after the first charge. In addition, the migration of Li into the 4h site in the Na metallic layer contributes less to the occurrence of voltage hysteresis because of the suppression of the interlayer O-O dimer. These results are clearly elucidated using the combined-phase mixing enthalpies and chemical potentials during the biphasic reaction. To compare the Mn oxide with R = 2, Na_1-x[Li_1/6Mn_5/6]O₂ tuned with R = 5 was investigated using the same procedure, and all the impeding factors in restraining the nonhysteretic OR were not observed. Herein, we suggest two strategies based on three types of OR models: (i) exploiting the migration of Li ions for the suppression of the interlayer O-O dimer and (ii) modulating the Mn/Li ratio for controlling the OR participation, which provides an exciting direction for nonhysteretic oxygen capacities for SIBs and lithium-ion batteries.

Keywords: cathode; first-principles calculations; layered oxides; oxygen redox; sodium-ion batteries; voltage hysteresis.