Mehdi Rezaee1,Hana Yoon2,Yeong A Lee2,Kanghoon Yim2,Rizcky Tamarany2,Chanwoo Lee2,Valerie McGraw3,Takashi Taniguchi4,Kenji Watanabe4,Philip Kim5,Chung Yul Yoo6,Kwabena Bediako3
Harvard Univeristy1,Korea Institute of Energy Research2,University of California Berkeley3,National Institute for Materials Science4,Harvard University5,Mokpo National University6
Mehdi Rezaee1,Hana Yoon2,Yeong A Lee2,Kanghoon Yim2,Rizcky Tamarany2,Chanwoo Lee2,Valerie McGraw3,Takashi Taniguchi4,Kenji Watanabe4,Philip Kim5,Chung Yul Yoo6,Kwabena Bediako3
Harvard Univeristy1,Korea Institute of Energy Research2,University of California Berkeley3,National Institute for Materials Science4,Harvard University5,Mokpo National University6
Paradigm shifts in batteries, ion separation, electronics, and myriad other technologies will require isolation and identification of the fundamental electrochemical characteristics of 2D heterointerfaces to enable rational materials design. To this end, we prepare individual vdW intercalation heterostructures of graphene and transition metal dichalcogenide (TMDC) layers that are encapsulated between layers of inert hexagonal boron nitride (hBN). We establish several operando experimental tools such as Hall voltammetry and intercalation frontier imaging to monitor the course of the electro-intercalation reaction at the mesoscopic 2D heterointerfaces. The high quality of our 2D intercalated heterostructures permits us to use low-temperature quantum transport methods in conjunction with spectroscopy to identify the fundamental layer capacities and equilibrium potentials of individual 2D. Particularly, we demonstrate the intercalation of AlCl<sub>4</sub><sup>– </sup>ions into van der Waals heterostructure layers consisting of deterministically stacked hexagonal boron nitride (hBN) and few layer graphene. We use magnetoresistance charge transport and <i>operando</i> optical microscopy to evaluate the dynamics of intercalation processes in atomically thin samples. We develop a colorimetric method to estimate the diffusion coefficient. The diffusion coefficient for AlCl<sub>4</sub><sup>–</sup>, measured in 2D graphitic hosts approaches 10<sup>–5</sup> cm<sup>2</sup> s<sup>–1</sup> at 320 K, establishing the intrinsic upper limit. These atomically thin single crystal measurements are compared to the cycling response of a high-performance rechargeable Al battery consisting of few-layer graphene–multiwall carbon nanotube composite cathode. Our results thus establish the distinction between intrinsic and ensemble electrochemical behavior in Al-based batteries and show that engineering ion transport to enhance diffusivity in these devices can yet lead to vast improvements in battery performance.