Ultrathick GeP Anode To Balance the Extreme Load and Compliance for High Areal Capacity Flexible Sodium-Ion Batteries.

The ever-growing application of miniaturized electric devices calls for the manufacturing of energy storage systems with a high areal energy density. Thick electrode design is a promising strategy to acquire high areal energy density by enhancing active mass loading and minimizing inactive components. However, the sluggish reaction kinetics and poor electrode mechanical stability that are accompanied by the increased electrode thickness remain unsolved problems. Herein, for the first time, we propose a novel chemical cross-linking strategy to fabricate GeP thick electrodes with adjustable electrode thicknesses and active mass loadings for high areal capacity sodium-ion batteries (SIBs). The chemical cross-linking between carboxylic multiwalled carbon nanotubes (CNTs) and pyrolysis cellulose nanofibers (CNFs) forms a 3D network that encloses GeP nanoparticles, which guarantees fast charge transfer, efficient stress relief, and alleviated volume expansion/shrinkage of the electrode. The hierarchical porous structure generates numerous interconnected channels for unfettered Na+ diffusion, ensuring uncompromised reaction kinetics as the electrode thickness increases. As a result, the ultrathick 1031 µm GeP@C-CNTs-CNFs electrode featuring a mass loading of 18.3 mg cm-2 delivers an ultrahigh areal capacity of 10.58 mAh cm-2 accompanied by superior cycling stability, which outperforms all reported Ge-based electrodes (generally below 1.5 mAh cm-2). This work sheds insightful light on designing high areal capacity flexible thick electrodes for the applications of miniaturized electric devices.

Tunable Hollow Nanoreactors for In Situ Synthesis of GeP Electrodes towards High-Performance Sodium Ion Batteries.

The practical application of germanium phosphide (GeP) in battery systems is seriously impeded referring to the sluggish reaction kinetics and severe volume change. Nanostructure design that elaborately resolves the above issues is highly desired but still remains a big challenge. Herein, unique hollow nanoreactors assembled with nitrogen-doped carbon networks for in situ synthesis of the GeP electrodes are proposed for the first time. Such nanoreactors form a self-supported conductive network, ensuring sufficient electrolyte infiltration and fast electron transport. They restrain crystal growth and accommodate the volume expansion of GeP simultaneously. Reaction kinetics and confinement effect are optimized through nanoreactor size regulation. The optimized GeP electrode has high reversible capacities and outstanding cyclability and rate performance for sodium storage, outperforming most previously reported phosphides.