1成果简介
　　水凝胶电解质被视为高性能水系锌离子电池（ZIBs）的有力候选材料，但其常难以兼顾反应动力学与Zn²⁺沉积稳定性。本文，武汉大学 陈朝吉教授、四川大学 张伟副研究员等在《ACS Nano》期刊发表名为“A Bioinspired Gradient Hydrogel Electrolyte Network with Optimized Interfacial Chemistry toward Robust Aqueous Zinc-Ion Batteries”的论文，研究受关节软骨启发，我们开发了一种梯度网络水凝胶电解质，由聚乙烯醇（PVA）、纤维素纳米纤维（CNF）和氧化石墨烯（GO）组成，用于ZIBs。
　　低网络密度PVA/CNF （PC）水凝胶层（阴极侧）具有广泛的通道和较高的含水量，确保了离子的快速传输，而与锌阳极接触的界面水凝胶层则呈现高密度PVA/CNF/GO（PCG）网络，富含羧基和羟基，这有利于Zn2+的脱溶剂化、降低水的活性并均匀化Zn2+的流动。此外，GO中的极性含氧基团赋予其介电和电子负性特性，共同提升了水凝胶电解质的Zn²⁺转移数和离子电导率。借助这种梯度网络结构和调控的界面化学，水凝胶电解质能够有效稳定Zn阳极，同时加速反应动力学。因此，水凝胶电解质使Zn对称电池在1 mA cm–2电流密度下超过2200小时的测试中展现出卓越的稳定性，而Zn–MnO₂全电池在各种外部损伤条件下也表现出增强的倍率性能和安全性。总体而言，本研究为高性能ZIBs提供了可靠的仿生水凝胶电解质设计策略。
　　2图文导读 

　　图1. Gradient-networked hydrogel electrolyte inspired by natural cartilage. (a) Schematic illustration of the “cartilage-inspired” gradient-networked hydrogel electrolyte for stabilizing the Zn anode. (b) Optical microscopy image of articular cartilage. (c) Photograph and (d) scanning electron microscopy (SEM) image of the PCG20–PC5 hydrogel.

　　图2. Theoretical simulation and characterization of Zn2+ transport and deposition behavior in different hydrogel electrolytes. (a) ESP maps of the H2O, PVA, CNF, and GO molecules. (b) The DFT calculations for the binding energies of Zn2+ to PVA, CNF, and GO molecules. (c) RDFs and corresponding coordination numbers for Zn–O (H2O) of the PC5, PC10, PC20, and PCG20 hydrogel electrolytes. (d) Arrhenius curves and corresponding desolvation activation energy values of Zn-symmetric cells with the hydrogel electrolytes. (e) Low-field nuclear magnetic resonance (LF-NMR) curves of the hydrogel electrolytes. (f) Tafel plots of Zn-symmetric cells with the hydrogel electrolytes. (g) Ionic conductivity of the PC5, PC10, PC20, PC20–PC5, and PCG20–PC5 hydrogel electrolytes. (h) Voltage profiles of Zn plating at 1 mA cm–2 on Cu foil with the hydrogel electrolytes.

　　图3. Long-term stability of Zn anodes with the different hydrogel electrolytes. (a) Voltage profiles of the Zn-symmetric cells with the PC5, PC10, PC20, PC20–PC5, and PCG20–PC5 hydrogel electrolytes at a current density of 5 mA cm–2 with a cycling capacity of 1 mAh cm–2. Voltage profiles of the Zn-symmetric cells with the PC10, PC20–PC5, and PCG20–PC5 hydrogel electrolytes (b) at various current densities with a cycling capacity of 1 mAh cm–2 and (c) at a current density of 1 mA cm–2 with a cycling capacity of 1 mAh cm–2. (d) Comparison of the lifespans of Zn anodes with the PCG20–PC5 hydrogel electrolyte with recently reported studies on the hydrogel electrolytes. (e) SEM images and (f) XRD patterns of the Zn electrodes after 200 plating/stripping cycles (5 mA cm–2, 1 mAh cm–2) in the PC10, PC20–PC5, and PCG20–PC5 hydrogel electrolytes. (g) Voltage profiles and (h) Coulombic efficiencies of asymmetrical Zn–Cu batteries with the PC10, PC20–PC5, and PCG20–PC5 hydrogel electrolytes at a cutoff potential of 0.8 V under 5 mA cm–2 within 1 mAh cm–2.

　　图4. Exploration of Zn plating behaviors in the PC20, PC20–PC5, and PCG20–PC5 hydrogel electrolytes. (a) CA curves at a potential of −150 mV and (b) Zn2+ transference numbers of the Zn-symmetric cells using the PC10, PC20–PC5, and PCG20–PC5 hydrogel electrolytes. (c) In situ optical microscopy images of Zn electrodes plating in the PC10, PC20–PC5, and PCG20–PC5 hydrogel electrolytes under a constant deposition current density of 10 mA cm–2 for various times. (d) Confocal laser scanning microscopy (CLSM) images of the Zn electrodes after 20 min of plating in the PC10, PC20–PC5, and PCG20–PC5 hydrogel electrolytes. (e) XRD patterns of the Zn electrode plating in the PCG20–PC5 hydrogel electrolytes under a constant deposition current density of 10 mA cm–2 for various times. (f) Simulated electric/ionic field distributions for PC10, PC20–PC5, and PCG20–PC5 systems based on schematic and simplified models.

　　图5. Electrochemical performance of Zn–MnO2 ZIBs. (a) CV curves at 0.2 mV/s, (b) GCD curves at 0.15 A g–1, (c) rate performance, (d) Nyquist plots, and (e) the long-term cycling performance of the coin ZIBs with the PC10, PC20–PC5, and PCG20–PC5 hydrogel electrolytes. (f) Capacity retention of the PCG20–PC5-based ZIB after charging to 1.8 V, resting for 72 h, and discharging to 1 V. (g) Capacity retention of the PCG20–PC5-based Zn–MnO2 pouch battery under different bending angles. (h) Digital photographs of a LED night light powered by the PCG20–PC5-based Zn–MnO2 pouch battery under various external damage (Wuhan University logo used with permission).
　　3小结
　　综上所述，我们开发了一种基于聚乙烯醇（PVA）、碳纳米纤维（CNF）和氧化石墨烯（GO）的具有梯度网络结构和优化界面化学的全新水凝胶电解质。实验和计算研究表明，梯度网络水凝胶电解质中具有不同功能的独特水凝胶层——低网络密度水凝胶电解质层确保了Zn2+的快速传输，而高网络密度水凝胶电解质层则促进了Zn2+的脱溶剂化，减轻了不利的Zn腐蚀，并均匀化了Zn2+的流量。高网络密度水凝胶电解质层中的GO还提供了另一项显著功能，即提高Zn2+的转移数和离子电导率。借助这些协同功能，水凝胶电解质可诱导Zn2+离子的均匀快速沉积，从而抑制Zn阳极上的Zn树枝状生长和副反应，同时不影响反应动力学。这种协同功能的水凝胶电解质使Zn对称电池具有卓越的循环寿命（在1 mA cm–2下超过2200小时），并使Zn–Cu不对称电池具有优异的镀/剥离可逆性（在2800个循环中平均CE为99.72%）。此外，采用PCG20–PC5水凝胶电解液的Zn–MnO₂全电池展现出长期循环稳定性（800次循环后容量衰减仅为0.013%）和增强的倍率性能。令人印象深刻的是，组装的软包电池在多种环境下表现出卓越的韧性和安全性，证实其在多种实际应用中具有巨大潜力。我们以自然为灵感构建的结构化多功能水凝胶电解液策略，为开发耐用、安全且高性能的水系锌电池开辟了充满希望的途径。
　　文献：