Kim Jae Jin, Zhou Chun, Mane Anil U, Suh Hyo Seon, Kim Soojeong, Shi Bing, Fenter Paul, Elam Jeffrey W, Nealey Paul F, Lee Byeongdu, Fister Timothy T
Pritzker School of Molecular Engineering, University of Chicago, 5640 South Ellis Avenue, Chicago, Illinois 60637, United States.
Interuniversity Microelectronics Centre, Kapeldreef 75, 3001 Leuven, Belgium.
ACS Nano. 2022 Apr 26;16(4):5384-5392. doi: 10.1021/acsnano.1c08599. Epub 2022 Mar 31.
In-plane tungsten oxide nanostructures, including hexagonally patterned cylinders and holes in a matrix, were fabricated sequential infiltration synthesis (SIS) on self-assembled block copolymer templates. Using the tailored morphology and porosity of these model electrodes with grazing incidence small-angle X-ray scattering, the intrinsic structural change of nanoscale active materials during the conversion reaction of WO + 6Li ↔ W + 3LiO was investigated at controlled electrochemical conditions. Reversible electrode volume expansion and contraction was observed during lithiation and delithiation cycles, respectively. The potential where the electrode's thickness expansion started was ∼1.6 V, which is close to the thermodynamically expected one for the conversion reaction of WO with lithium (1.65 V). The temporal evolution of the electrode volume at constant electrode potentials revealed high overpotential for bulk lithiation and slow conversion reaction kinetics, despite the tailored porosity of the SIS electrodes. Oxide cylinders showed a smaller overall electrode thickness change, likely due to unconstrained lateral volume change, as compared to a matrix with holes. On the other hand, better connectivity and guided volume change of the latter electrode morphology provided improved cycling stability. In addition, heterogeneity in an electrode, from internal pores and density gradients, was found to aggravate the fragmentation of the electrode during the conversion reaction. Insights into oxide conversion reaction kinetics and the relationship between electrode mesostructure and cycling behavior obtained from this study can help guide the more rational design of conversion electrodes for high-performing batteries.
通过在自组装嵌段共聚物模板上进行连续浸润合成（SIS），制备了平面内氧化钨纳米结构，包括六边形图案化的圆柱体和基质中的孔洞。利用掠入射小角X射线散射对这些模型电极的定制形态和孔隙率，在可控的电化学条件下研究了WO + 6Li ↔ W + 3LiO转化反应过程中纳米级活性材料的固有结构变化。在锂化和脱锂循环过程中分别观察到了可逆的电极体积膨胀和收缩。电极厚度开始膨胀时的电位约为1.6 V，这与WO与锂转化反应的热力学预期值（1.65 V）接近。在恒定电极电位下电极体积的时间演变表明，尽管SIS电极具有定制的孔隙率，但整体锂化存在高过电位且转化反应动力学缓慢。与有孔洞的基质相比，氧化物圆柱体的整体电极厚度变化较小，这可能是由于横向体积变化不受约束。另一方面，后一种电极形态更好的连通性和引导的体积变化提供了更好的循环稳定性。此外，发现电极内部孔隙和密度梯度导致的不均匀性会加剧转化反应过程中电极的破碎。从这项研究中获得的关于氧化物转化反应动力学以及电极介观结构与循环行为之间关系的见解，有助于指导高性能电池转化电极的更合理设计。
