Kim Hyungjun, Yoon Sangho, Koo Sojung, Lee Jinwoo, Kim Jongbeom, Cho Maenghyo, Kim Duho
Departemnt of Mechanical Engineering, Seoul National University, Gwanak-ro 1, Gwanak-gu, Seoul 08826, Republic of Korea.
Department of Mechanical Engineering (Integrated Engineering Program), Kyung Hee University, 1732, Deogyeong-daero, Giheung-gu, Yongin-si, Gyeonggi-do 17104, Republic of Korea.
ACS Appl Mater Interfaces. 2022 Feb 23;14(7):9057-9065. doi: 10.1021/acsami.1c22521. Epub 2022 Feb 14.
Nonhysteretic redox capacity is a critical factor in achieving high energy density without energy loss during cycling for rechargeable battery electrodes, which has been considered a major challenge in oxygen redox (OR) for Li-excess layered oxide cathodes for lithium-ion batteries (LIBs). Until recently, transition metal migration into the Li metal layer and the formation of O-O dimers have been considered major factors affecting hysteretic oxygen capacity. However, Li-excess layered oxides, particularly Ru oxides, exhibit peculiar voltage hysteresis that cannot be sufficiently described by only these factors. Therefore, this study aims to unlock the critical impeding factors in restraining the non-polarizing oxygen capacity of Li-excess layered oxides (herein, LiRuO) that exhibit reversible OR reactions. First, LiRuO undergoes an increase in the chemical potential fluctuation as both the thermodynamic material instability and vacancy content increase. Second, the chemical compression of O-O bonds occurs at the early stage of the OR reaction (0.5 ≤ ≤ 0.75) for LiRuO, leading to flexible voltage hysteresis. Finally, in the range of 0.75 ≤ ≤ 1.0, for LiRuO, the formation of an O(2p)-O(2p)* antibonding state derived from the structural distortion of the RuO octahedron leads to the irreversibility of the OR reaction and enhanced voltage hysteresis. Consequently, our study unlocks the new decisive factor, namely, the structural distortion inducing the O(2p)-O(2p)* antibonding state, of the hysteretic oxygen capacity and provides insights into enabling the full potential of the OR reaction for Li-excess layered oxides for advanced LIBs.
非滞后氧化还原容量是可充电电池电极在循环过程中实现高能量密度且无能量损失的关键因素，这被认为是锂离子电池（LIB）富锂层状氧化物阴极氧还原（OR）中的一个主要挑战。直到最近，过渡金属迁移到锂金属层以及O - O二聚体的形成一直被认为是影响滞后氧容量的主要因素。然而，富锂层状氧化物，特别是钌氧化物，表现出特殊的电压滞后现象，仅这些因素无法充分描述。因此，本研究旨在揭示抑制表现出可逆OR反应的富锂层状氧化物（本文中为LiRuO）非极化氧容量的关键阻碍因素。首先，随着热力学材料不稳定性和空位含量的增加，LiRuO的化学势波动增大。其次，对于LiRuO，在OR反应的早期阶段（0.5≤≤0.75）发生O - O键的化学压缩，导致灵活的电压滞后。最后，在0.75≤≤1.0的范围内，对于LiRuO，由RuO八面体结构畸变衍生的O(2p) - O(2p)*反键态的形成导致OR反应的不可逆性和增强的电压滞后。因此，我们的研究揭示了滞后氧容量的新决定性因素，即诱导O(2p) - O(2p)*反键态的结构畸变，并为充分发挥先进LIBs富锂层状氧化物OR反应的全部潜力提供了见解。
