Hase Yoko, Uyama Takeshi, Nishioka Kiho, Seki Juntaro, Morimoto Kota, Ogihara Nobuhiro, Mukouyama Yoshiharu, Nakanishi Shuji
Toyota Central R&D Laboratories, Inc., 41-1 Yokomichi, Nagakute, Aichi 480-1192, Japan.
Research Center for Solar Energy Chemistry, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan.
J Am Chem Soc. 2022 Jan 26;144(3):1296-1305. doi: 10.1021/jacs.1c10986. Epub 2022 Jan 11.
The large overpotential of nonaqueous Li-O batteries when charging causes low round-trip efficiency and decomposition of the electrode materials and electrolyte. The origins of this overpotential have been enthusiastically explored to date; however, a full understanding has not yet been reached because of the complexity of multistep reaction mechanisms. Here, we applied structural and electrochemical analysis techniques to investigate the reaction step that results in the increase of the overpotential when charging. Rietveld refinement of powder X-ray diffraction showed that a Li-deficient phase of LiO, LiO, formed when discharging and was present over the course of charging. The galvanostatic intermittent titration technique revealed that the rate-determining process in the first step of charging was a solid-solution type of delithiation. The chemical diffusion coefficient of Li ions in LiO, , decreases as the cell voltage increases, which in turn leads to a decrease in the oxidation rate of LiO. Under galvanostatic conditions, the deceleration of oxidation induces further increase of the cell voltage; therefore, an intrinsic mechanism of positive feedback to increase the cell voltage occurs in the first step. The results demonstrate that the continuity of the first step can be extended by the suppression of changes in any of the elements of the positive feedback loop, i.e., the oxidation rate, cell voltage, or .
非水锂氧电池充电时的高过电位导致往返效率低以及电极材料和电解质分解。迄今为止，人们一直在积极探索这种过电位的起源；然而，由于多步反应机制的复杂性，尚未达成全面的理解。在此，我们应用结构和电化学分析技术来研究导致充电时过电位增加的反应步骤。粉末X射线衍射的Rietveld精修表明，放电时形成了LiO的锂缺陷相LiO，并在充电过程中存在。恒电流间歇滴定技术表明，充电第一步中的速率决定过程是固溶体型的脱锂过程。随着电池电压升高，LiO中锂离子的化学扩散系数降低，这进而导致LiO氧化速率降低。在恒电流条件下，氧化减速会导致电池电压进一步升高；因此，在第一步中会出现增加电池电压的正反馈内在机制。结果表明，通过抑制正反馈回路中任何一个元素的变化，即氧化速率、电池电压或 ，可以扩展第一步的连续性。
