Electrospinning Machine| Modulating Zn2+ Desolvation and Deposition with Fluorine‐Nitrogen Co‐doped Carbon Dot Interlayers for High‐Rate Aqueous Zinc‐Ion Batteries

Aqueous zinc-ion batteries (AZIBs) are regarded as a cutting-edge direction for next-generation energy storage systems due to low cost, high volumetric capacity, and intrinsic safety. However, their zinc anode interface failure issues (dendrite growth, electrochemical corrosion, and hydrogen evolution reaction) lead to a significant decrease in CE and cycle life. Constructing an artificial interface layer can physically block electrolyte corrosion and suppress dendrites through electric field regulation and ion flux redistribution. However, traditional binder-based interface layers struggle to synergistically inhibit dendrites/HER/passivation due to poor component compatibility and limited ion transport. Developing a self-supporting interface layer system that combines structural uniformity, high Zn²⁺ transference number, and multi-mechanism synergy is the core path to break through the application bottleneck of AZIBs.

Recently, Professor Wei Ai and Associate Researcher Ke Wang from Northwestern Polytechnical University published their latest research, titled "Modulating Zn2+ Desolvation and Deposition with Fluorine‐Nitrogen Co‐doped Carbon Dot Interlayers for High‐Rate Aqueous Zinc‐Ion Batteries" in the journal Advanced Functional Materials. The researchers constructed a polyacrylonitrile (PAN) matrix embedded with fluorine-nitrogen co-doped carbon dot composite protective layer (PAN/FN-CDs) in situ on the zinc metal surface via an electrostatic spinning process. This protective layer combines high mechanical strength and controllable hydrophobicity, enabling real-time adaptation to the volume fluctuations of the zinc anode during cycling. Its dense 3D network structure effectively blocks contact between the electrolyte and the electrode interface, suppressing side reactions. Simultaneously, the abundant zincophilic groups (e.g., -CHO, -CN, and -F) in the protective layer provide nucleation sites for uniform zinc deposition, achieving synergistic regulation of Zn²⁺ deposition behavior by reducing the desolvation energy barrier and nucleation overpotential.

Figure 1: Fabrication and structure of the PAN/FN-CDs composite protective layer for zinc anode.

Figure 1a shows the in-situ electrospinning preparation process of the self-supporting PAN/FN-CDs composite protective layer. FN-CDs were synthesized macro-scale via hydrothermal method, with a particle size <3 nm (Fig. 1b), exhibiting both ethanol solubility and excellent hydrolytic stability. FTIR and XPS analyses indicate their surface is rich in zincophilic groups like -CHO, -CN, and -F. The material surface is negatively charged, enabling efficient regulation of Zn²⁺/SO₄²⁻ transport. SEM shows a three-dimensional flexible nanonetwork (diameter ~300 nm), effectively buffering electrode volume changes (Fig. 1e-f). FN-CDs are uniformly dispersed within the PAN fibers (Fig. 1h), leading to a significant decrease in the charge transfer impedance of the composite electrode. The protective layer has a hydrophobic interface that significantly suppresses side reactions, and its mechanical strength is superior to traditional glass fiber, meeting the demands of high-current cycling. This design provides an innovative solution for highly stable zinc anodes by optimizing ion transport kinetics and inhibiting dendrite growth.

Figure 2: Electrochemical performance of modified zinc anodes and analysis of reaction kinetic mechanisms.

The protective effect of the PAN/FN-CDs modification layer was verified through tests on Zn//Zn symmetric cells and Cu//Zn asymmetric cells. The Zn@PAN/FN-CDs symmetric cell achieved >5000 hours of cycling (bare Zn failed at 150 hours, Zn@PAN failed at 500 hours), with the lowest voltage hysteresis in the range of 1-10 mA cm⁻² (Fig. 2a-b). It remained stable for 3000 h even at a high current density (10 mA cm⁻²) (Fig. 2c), attributed to the zincophilic surface and uniform nucleation site design of PAN/FN-CDs (Fig. S10). EIS analysis showed the charge transfer resistance (Rct) of cycled Zn@PAN/FN-CDs was significantly lower than the control groups (Fig. 2d). CV tests showed reduced deposition overpotential and enhanced response current (Fig. 2e), confirming improved kinetic performance. In Cu//Zn cell tests, the initial Coulombic efficiency of Zn@PAN/FN-CDs reached 95.5%, stabilizing at 99.5% after 10 cycles, with a cycle life superior to bare Zn (350 cycles) and Zn@PAN (670 cycles) (Fig. 2f-g). Furthermore, the hydrogen evolution potential of Zn@PAN/FN-CDs shifted negatively to -1.84 V vs SCE (bare Zn -1.79 V, Zn@PAN -1.75 V), and the corrosion current density decreased by 75% (1.898 vs 7.522 mA cm⁻²) (Fig. 2h-i). Studies on zinc deposition behavior showed that Zn@PAN/FN-CDs switched from a two-dimensional diffusion mode to a three-dimensional diffusion mode after 30 seconds in chronoamperometry tests (Fig. 2j), with a Zn²⁺ transference number reaching 0.74 (bare Zn 0.22, Zn@PAN 0.53) (Fig. 2k). Its flexible 3D network structure and zincophilic groups (-CHO, -CN, -F) synergistically promoted rapid Zn²⁺ migration and uniform deposition.

Figure 3: Regulation mechanism of the PAN/FN-CDs composite protective layer on Zn2+ deposition behavior.

The Zn@PAN/FN-CDs anode maintained structural integrity at both 1 mA cm⁻² and 10 mA cm⁻² current densities, remaining smooth even during mechanical stripping, whereas the bare Zn surface showed rough zinc flakes with disordered distribution (Fig. 3a). Binding energy analysis showed that the binding energy of -C≡N and -CHO groups in PAN/FN-CDs to Zn²⁺ (-0.48/-0.50 eV) was significantly higher than that of bare Zn (-0.07 eV), guiding uniform zinc ion deposition (Fig. 3d). XRD results showed the modified zinc anode's (002)/(101) crystal plane intensity ratio reached 1.29, 4.8 times that of bare Zn (0.27) (Fig. 3e-f). Wide-angle diffraction and pole figure analysis further confirmed its preferred orientation of the (002) crystal plane (Fig. 3g-j). Surface energy calculations indicated that the F-Zn interaction reduced the energy of the (002) plane by 0.046 eV (Fig. 3k-l), promoting preferential deposition on the low-energy plane. In-situ observation showed the modified anode maintained uniform deposition for 60 minutes at 10 mA cm⁻², while bare Zn showed corrosion within 10 minutes (Fig. 3m-n).

Figure 4: Multi-level synergistic regulation mechanism of the PAN/FN-CDs functional coating on the zinc surface.

As shown in Figure 4a, the bare Zn anode surface is prone to hydrogen evolution reaction (H₂O molecules reacting with zinc to generate byproducts) and forms dendritic deposits, leading to uneven surface morphology; whereas the zinc anode covered with the PAN/FN-CDs layer (Zn@PAN/FN-CDs) effectively inhibits dendrite nucleation and mitigates interface corrosion. This functional coating works synergistically through the following mechanisms: Strong coordination regulation: The coating is rich in electronegative groups like -C≡N, -C=O, and -F, forming strong coordination with Zn²⁺, promoting the desolvation of hydrated zinc ions ([Zn(H₂O)₆]²⁺). 3D hydrophobic barrier: The 3D network structure composed of PAN nanofibers and FN-CDs has excellent hydrophobicity, reducing water molecule contact and inhibiting electrolyte decomposition and zinc corrosion.By analyzing the Raman spectra of the zinc/electrolyte interface (Fig. 4b), it was found that the PAN/FN-CDs layer significantly enhanced the binding of [Zn²⁺-SO₄²⁻] ion pairs. The proportion of contact ion pairs (CIP) at the coating interface reached 34.1% (only 25.3% for bare Zn), while the peak area of strong O─H hydrogen bonds decreased (30.8%→25.3%), indicating the coating optimized the solvation structure of Zn²⁺ by reconstructing the interfacial water network. Based on Arrhenius equation analysis (Fig. 4c), the activation energy (Ea=14.7 kJ·mol⁻¹) of Zn@PAN/FN-CDs was significantly lower than that of bare Zn (34.2 kJ·mol⁻¹), indicating the coating can rapidly strip the solvent shell of hydrated zinc ions, accelerating the desolvation process. Furthermore, DFT calculations (Fig. 4d) showed that the coating interface reduced the stepwise desolvation energy barrier of [Zn(H₂O)₆]²⁺, further confirming its advantage in enhancing zinc ion diffusion kinetics.

Figure 5: Full cell performance.

To verify the practical application potential of the Zn@PAN/FN-CDs anode, δ-MnO₂ was selected as the cathode to assemble a full cell (Fig. 5a). Cyclic voltammetry tests showed similar curves for full cells with different anodes (Fig. 5b), indicating the PAN/FN-CDs layer has no significant impact on the redox reactions. Meanwhile, the Zn@PAN/FN-CDs//δ-MnO₂ cell exhibited higher current density and lower voltage polarization, indicating its excellent zinc storage capability and ion diffusion kinetics. After resting for 48 hours, the Coulombic efficiency of the Zn@PAN/FN-CDs//δ-MnO₂ cell reached 94.4%, significantly better than the Zn@PAN (87.8%) and bare Zn (86.0%) systems (Fig. 5c), confirming this protective layer effectively suppresses self-discharge. Within the current density range of 0.5-10 A g⁻¹, the Zn@PAN/FN-CDs//δ-MnO₂ cell exhibited stable rate performance (Fig. 5d), with capacity maintained between 98.6-310.2 mAh g⁻¹. In long-term cycling tests at 1 A g⁻¹ (Fig. 5e), the cell maintained a capacity of 200.3 mAh g⁻¹ after 1500 cycles. After disassembling the cells, particle agglomeration was found on the surfaces of the bare Zn and Zn@PAN anodes, while Zn@PAN/FN-CDs remained smooth (Fig. 5f-g). XRD patterns showed the presence of byproduct Zn₄SO₄(OH)₆·4H₂O in the former two (Fig. 5h), further confirming the effectiveness of the protective layer. Additionally, a pouch cell based on this anode stably cycled 200 times at 1.0 A g⁻¹ (Fig. 5i), achieving a capacity of 120 mAh g⁻¹ after activation, and successfully powered multiple LED lights (Fig. 5j), demonstrating the application potential for high-safety, sustainable energy storage systems.

Paper link: https://advanced.onlinelibrary.wiley.com/doi/10.1002/adfm.202513796