Designing Anti‐Swelling Nanocellulose Separators with Stable and Fast Ion Transport Channels for Efficient Aqueous Zinc‐Ion Batteries

Abstract

Separators swelling in aqueous electrolytes can cause inhomogeneous ion flux and unregulated dendrite propagation, yet the corresponding phenomenon and mitigation strategy are rarely studied. This article deals with the issue of pore structure variation caused by separator swelling in aqueous zinc‐ion batteries (AZBs) by employing nanocellulose separator as a representative example. A multifunctional separator composed of Zr4+‐hydrolysate‐coated nanocellulose (Zr‐CNF) is developed by in situ hydrolysis of Zr4+, which demonstrates excellent swelling resistance, pore‐structure stability, and percolating porosity due to cross‐linking and hydrogen bond shielding effect. Consequently, the homogeneous Zn‐ion flux, high ionic conductivity, and Zn2+ transfer number are maintained upon cycling. Moreover, the amorphous ZrO containing coating induces a homogeneous directional electric field around the interface, accelerating the Zn2+ influx, reducing the nucleation overpotential, and promoting homogeneous nucleation for Zn deposition. The Zr‐CNF separator enable dendrite‐free Zn anode with high Coulombic efficiency (99.7%) and exceptional cyclability for 680 h under 5 mA cm−2/5 mAh cm−2. The feasibility of the Zr‐CNF separator is verified in PANI/V2O5‐based AZBs and activated carbon‐based Zn‐ion capacitors. This study provides a facile approach to address separator swelling issue, enlightening novel insights into the efficient and sustainable aqueous battery technologies in the future.

Functionalized Non-Glass Fiber Nanoporous Separator for High-Performance Aqueous Zinc Ion Batteries

“…This is achieved through structural enhancements and the addition of modification materials. 74 For instance, Wang et al 75 developed a multifunctional separator, Zr 4+ -hydrolysate-coated nanocellulose (Zr-CNF), through in situ hydrolysis of Zr 4+ . This separator exhibited antiswelling properties, stable pore structure, and permeability porosity due to cross-linking and hydrogen-bonding shielding (Figure 6a).…”

“…(a) Schematic diagram of the evolution of pore structural for both separators. Reproduced with permission from ref . Copyright 2023 Wiley-VCH.…”

Advances of Nanomaterials for High-Efficiency Zn Metal Anodes in Aqueous Zinc-Ion Batteries

“…Building on this, Yang et al utilized ion coordination and hydrolytic precipitation to cross-link Zr 4+ onto nanocellulose, constructing a dendrite-resistant zirconium-hydrolysate-coated-nanocellulose (Zr-CNF) separator with nanoscale pore sizes and stable ion diffusion channels. 222 Because of their robust porous structure, Zr-CNF separators exhibit excellent antiexpansion properties and satisfied structural stability, which guarantees efficient ion movement (Figure 13d). Furthermore, Zr 4+ hydrolyzes to form amorphous Zr−O coatings with dielectric properties on the nanocellulose surface, creating a welldispersed electric field for uniform Zn 2+ plating/stripping and hindering dendrites generation.…”

Amorphous Cellulose Electrolyte for Long Life and Mechanically Robust Aqueous Structural Batteries

“…While there have been numerous studies employing cellulose in aqueous Zn batteries, they are mainly cellulose‐based separators formed through assembling fibrous cellulose (e.g., cellulose nanofibrils) into an entangled porous network. [ 20–22 ] However, porous assembly of cellulose fibers without further chemical modifications would experience tremendous mechanical decay upon contact with aqueous electrolyte solutions. [ 21,23,24 ] Furthermore, while they offer a sustainable alternative to commercial polyolefin‐based separators, issues of electrolyte leakage and water evaporation persist, unlike solid‐state polymer electrolytes.…”

“…[ 20–22 ] However, porous assembly of cellulose fibers without further chemical modifications would experience tremendous mechanical decay upon contact with aqueous electrolyte solutions. [ 21,23,24 ] Furthermore, while they offer a sustainable alternative to commercial polyolefin‐based separators, issues of electrolyte leakage and water evaporation persist, unlike solid‐state polymer electrolytes. [ 25,26 ]…”