Visualizing fast interlayer anisotropic lithium diffusion via single crystal microbattery

Abstract

<h2>Summary</h2> Ion insertion in host layered materials is the foundation of energy storage mechanism of commercial lithium-ion batteries. Contrary to general view that small lithium (Li) diffuses freely between large interlayer, here, we <i>in situ</i> visualize Li diffusion pathways into the layered germanium phosphide (GeP) crystal flake along different directions via a microbattery device. Surprisingly, a more preferential Li diffusion pathway along zigzag [010] direction than armchair [102] direction is observed, demonstrating a strong in-plane diffusion anisotropy up to 7.0. And an interlayered Li diffusion coefficient of 3.4 × 10⁻⁷ cm² s⁻¹ is obtained for GeP flake, over 1,000 times faster than that measured for graphite flake (2.4 × 10⁻¹¹ cm² s⁻¹), suggesting a high potential of GeP as an attractive fast-charging material. The visualizing and quantitative strategy for the intrinsic diffusion process provides solid and scientific guidance on high-through material screening for fast-charging batteries.