Ye Yadong, Xie HuanYu, Yang Yinghui, Xie Yuansen, Lu Yuhao, Wang Jinxi, Kong Xianghua, Jin Song, Ji Hengxing
Department of Applied Chemistry, CAS Key Laboratory of Materials for Energy Conversion, University of Science and Technology of China, Hefei 230026, China.
Ningde Amperex Technology Limited (ATL), Ningde 352100, China.
J Am Chem Soc. 2023 Nov 1. doi: 10.1021/jacs.3c08711.
Electrochemical Li-alloying reactions with Li-rich alloy phases render a much higher theoretical capacity that is critical for high-energy batteries, and the accompanying phase transition determines the alloying/dealloying reversibility and cycling stability. However, the influence of phase-transition characteristics upon the thermodynamic properties and diffusion kinetic mechanisms among the two categories of alloys, solid-solutions and intermetallic compounds, remains incomplete. Here we investigated three representative Li-alloys: Li-Ag alloy of extended solid-solution regions; Li-Zn alloy of an intermetallic compound with a solid-solution phase of a very narrow window in Li atom concentration; and Li-Al alloy of an intermetallic compound. Solid-solution phases undertake a much lower phase-transition energy barrier than the intermetallic compounds, leading to a considerably higher Li-alloying/dealloying reversibility and cycling stability, which is due to the subtle structural change and chemical potential gradient built up inside of the solid-solution phases. These two effects enable the Li atoms to enter the bulk of the Li-Ag alloy to form a homogeneous alloy phase. The pouch cell of the Li-rich LiAg alloy pairs with a LiNiCoMnO cathode under an areal capacity of 3.5 mAh cm can retain 87% of its initial capacity after 250 cycles with an enhanced Coulombic efficiency of 99.8 ± 0.1%. While Li-alloying reactions and the alloy phase transitions have always been tightly linked in past studies, our findings provide important guidelines for the intelligent design of components for secondary metal batteries.
与富锂合金相发生的电化学锂合金化反应具有更高的理论容量，这对高能电池至关重要，且伴随的相变决定了合金化/脱合金化的可逆性和循环稳定性。然而，相变特性对固溶体和金属间化合物这两类合金的热力学性质和扩散动力学机制的影响仍不明确。在此，我们研究了三种具有代表性的锂合金：具有扩展固溶区的Li-Ag合金；具有金属间化合物且锂原子浓度固溶相窗口非常窄的Li-Zn合金；以及金属间化合物Li-Al合金。固溶相比金属间化合物具有低得多的相变能垒，导致锂合金化/脱合金化的可逆性和循环稳定性显著更高，这归因于固溶相内部形成的细微结构变化和化学势梯度。这两种效应使锂原子能够进入富锂LiAg合金的主体以形成均匀合金相。在面积容量为3.5 mAh cm²的情况下，富锂LiAg合金与LiNiCoMnO正极组成的软包电池在250次循环后可保持其初始容量的87%，库仑效率提高到99.8±0.1%。虽然在过去的研究中锂合金化反应和合金相变一直紧密相关，但我们的研究结果为二次金属电池组件的智能设计提供了重要指导。
