Park Sangeon, Lee Jaewoon, Kim Hyungjun, Chioi Gwanghyeon, Koo Sojung, Lee Jinwoo, Cho Maenghyo, Kim Duho
Department of Mechanical Engineering (Integrated Engineering Program), Kyung Hee University, 1732, Deogyeong-daero, Giheung-gu, Yongin-si, Gyeonggi-do 17104, Republic of Korea.
Department of Mechanical and Aerospace Engineering & Department of Mechanical Engineering, Seoul National University, 1 Gwanak-ro. Gwanak-gu, Seoul 08826, Republic of Korea.
ACS Appl Mater Interfaces. 2022 May 4;14(17):19515-19523. doi: 10.1021/acsami.2c02438. Epub 2022 Apr 22.
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[LiMn]O with a Mn/Li ratio () 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/O and O/O conditions reveal the monophasic (0.0 ≤ ≤ 4/6) and biphasic (4/6 ≤ ≤ 1.0) reactions in Na[LiMn]O, but each stability at = 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 = 2, Na[LiMn]O tuned with = 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.
人们对钠层状氧化物阴极中的氧还原（OR）反应进行了深入研究，以充分发挥其在实现钠离子电池（SIB）高能量密度方面的潜力。然而，对于基于OR的氧化物，在首次充电过程后的放电过程中，OR会引发较大的滞后电压，其内在原因尚不清楚。因此，在本研究中，对Mn/Li比（）为2的Na[LiMn]O中反应机理的基本原理进行了深入重新研究，以确定使OR活性极化的因素，并使用第一性原理计算提供导致无滞后氧容量的设计规则。基于热力学能量，O/O和O/O条件揭示了Na[LiMn]O中的单相（0.0≤≤4/6）和双相（4/6≤≤1.0）反应，但在=5/6时每种稳定性的观察结果不同。O - O键布居表明，层间O - O二聚体的形成是引发滞后氧容量的关键因素，而混合层中的O - O二聚体在首次充电后提供无滞后氧容量。此外，由于层间O - O二聚体的抑制，Li迁移到Na金属层中的4h位点对电压滞后的发生贡献较小。使用双相反应过程中的组合相混合焓和化学势清楚地阐明了这些结果。为了将=2的锰氧化物进行比较，使用相同程序研究了=5的Na[LiMn]O，未观察到抑制无滞后OR的所有阻碍因素。在此，我们基于三种类型的OR模型提出了两种策略：（i）利用Li离子的迁移来抑制层间O - O二聚体，以及（ii）调节Mn/Li比以控制OR参与，这为SIB和锂离子电池的无滞后氧容量提供了一个令人兴奋的方向。
