Electrospinning Machine | Graphite‐Modified PAN Separator with Electron Buffer Layer for Regulating Zn2+ Deposition in Aqueous Zinc‐Ion Batteries

Aqueous zinc-ion batteries have garnered significant attention due to their inherent advantages such as high safety, environmental friendliness, and low cost, demonstrating substantial application potential in electrochemical energy storage. However, zinc-ion batteries face critical challenges including dendrite growth and the formation of by-products. As a core component of the battery, the separator ensures efficient ion transport while preventing electrode short circuits, directly impacting the battery's safety and cycling stability.

Recently, Xin Wang's team at the Songshan Lake Materials Laboratory published their latest research results, "Graphite‐Modified PAN Separator with Electron Buffer Layer for Regulating Zn2+ Deposition in Aqueous Zinc‐Ion Batteries," in the journal Small Methods. The researchers used polyacrylonitrile (PAN) and graphite nanoparticles as precursors to design a modified PAN nanofiber separator (GPAN) via the electrospinning method. Graphite nanoparticles act as an electron buffer layer, accelerating interfacial charge transfer, dispersing excess charge from the electrode surface to the graphite particles, reducing polarization caused by charge accumulation, and suppressing the tip effect through electron consumption. The GPAN separator has a high Zn²⁺ transference number of up to 0.92 and an ionic conductivity of 11.7 mS cm⁻¹. At a high current density of 10 mA cm⁻², the Zn||Zn symmetric battery exhibited long-term stability (up to 400 hours). This work provides a simple and effective method for developing high-performance ZIBs by designing PAN-based separators with high ion transference numbers and functional properties to regulate Zn²⁺ deposition.

Fig. 1. a) Schematic diagram of the preparation of the GPAN separator. b) Deposition mechanisms of different separators in ZIBs.

Fig. 2. a, b) SEM images at different magnifications of the GPAN separator and PAN separator. c) Electrolyte uptake of different separators. d) FTIR spectra of the GPAN separator and PAN separator. e) Flexibility of the PAN-based separator. f) Thickness of the GPAN, PAN, and GF separators, respectively. g) Tensile strength of the GPAN, PAN, and GF separators.

Fig. 3. a) Tafel curves of batteries with different separators. b) XRD patterns of zinc anodes using GPAN, PAN, and GF separators after 100 cycles at a current density of 1 mA cm⁻² and a capacity of 1 mAh cm⁻². c) LSV curves of zinc anodes using GPAN, PAN, and GF separators at a scan rate of 1 mV s⁻¹. d) CA curves of Zn||Zn symmetric batteries using GPAN, PAN, and GF separators. e) First cycle overpotential of zinc deposition on bare copper using GPAN, PAN, and GF separators, respectively. f) EIS of the battery assembled with the GPAN separator before and after polarization and the corresponding i-t curve at a potential of 10 mV. g) Nyquist plots and calculated ionic conductivity of GPAN, PAN, and GF separators using two stainless steel electrodes. h) Comparison of ionic conductivity and zinc ion transference number for different separators. i) Arrhenius curves and corresponding activation energy for GPAN, PAN, and GF separators.

Fig. 4. a) Cycling performance of Zn||Zn symmetric batteries using different separators at a current density of 1 mA cm⁻² and a capacity of 1 mAh cm⁻². b) Cycling performance of Zn||Zn symmetric batteries using different separators at a current density of 10 mA cm⁻² and a capacity of 10 mAh cm⁻². c) Rate performance of Zn||Zn symmetric batteries using GPAN, PAN, and GF separators at different current densities. d) Surface morphology of pristine zinc foil. e-g) Surface morphology of zinc electrodes using GF, PAN, and GPAN separators, respectively, after 100 hours of cycling. h-j) LCSM images of zinc electrodes using GF, PAN, and GPAN separators, respectively, after 100 hours of cycling. k) Coulombic efficiency of Zn||Cu half-cells using different separators. l) Capacity-voltage profile of the battery using the GPAN separator.

Fig. 5. a-c) CV curves of full cells using GPAN, PAN, and GF separators, respectively, at different scan rates. d) EIS of full cells using GPAN, PAN, and GF separators, respectively. e) Rate performance of full cells using GPAN, PAN, and GF separators. f) Galvanostatic charge-discharge curves of the full cell using the GPAN separator at different currents. g) Long-term cycling performance of full cells using GPAN, PAN, and GF separators, respectively, at a current density of 1 A g⁻¹.

Research Conclusion
This paper designed a graphite nanoparticle-modified PAN separator prepared by electrospinning. The graphite nanoparticles serve as an electron buffer layer, accelerating interfacial charge transfer, dispersing excess charge from the electrode surface to the graphite particles, reducing polarization caused by charge accumulation, and optimizing zinc ion deposition behavior by suppressing the tip effect through electron consumption. To evaluate the ability of different separators to regulate zinc ion deposition, we conducted long-term cycling tests and rate performance tests on Zn||Zn symmetric batteries at different current densities. The results show that the GPAN separator has an ionic conductivity of up to 11.7 mS cm⁻¹ and a Zn²⁺ transference number of 0.92. The Zn||Zn symmetric battery using the GPAN separator achieved a long cycle life of 400 hours at a current density of 10 mA cm⁻² and a capacity of 10 mAh cm⁻². The Zn||Cu half-cell exhibited an excellent Coulombic efficiency of 99.32%. The Zn||NVO full cell showed a capacity retention rate of 74% after 1000 cycles at a current density of 1 A g⁻¹, demonstrating excellent cycling stability. It is anticipated that this GPAN separator with efficient ion transport channels will open an innovative path for the exploration of next-generation efficient aqueous zinc-ion batteries (ZIBs).

Paper link: https://onlinelibrary.wiley.com/doi/10.1002/smtd.202501055