Redefining Separator Design and Water Activity for High-Energy Zinc Batteries Using Covalent Organic Framework.

Abstract

Despite zinc metal batteries offering attractions such as natural abundance, safety, and sustainability, their widespread adoption is hindered by a critical, underexplored limitation: intrinsically low device-level energy density. While previous research has prioritized stabilizing zinc anodes to suppress dendrites, practical energy densities remain constrained by excessive inactive components (separators, electrolytes) that dominate device mass and volume. Conventional strategies, such as cell upscaling, exacerbate this issue by necessitating surplus electrolyte, leading to inflated electrolyte to capacity ratios (> 10 g Ah^-1) and poor specific/volumetric energy metrics (e.g., ∼5 Wh kg^-1). Current reporting practices, focusing on Ah or idealized active-material metrics, further obscure true performance, masking the urgent need for holistic design innovations. Crucially, lean-electrolyte operation, essential for high energy density, introduces unaddressed challenges like interfacial water depletion and activity mismanagement. This work bridges this gap by systematically unraveling failure mechanisms under lean conditions and pioneering a functional separator that optimizes water management and ion transport. By redefining hydrogen-bonding networks to mitigate water consumption and enable rapid infiltration, the developed COF@PAN separator achieves unprecedented energy densities (54.0 Wh kg^-1, 185.3 Wh L^-1) and cycle stability (over 800 cycles) in practical pouch cells. These insights and designs advance Zn metal batteries beyond lab-scale promises, positioning them as viable contenders for energy-dense, real-world applications.