Synergistically regulating the separator pore structure and surface property toward dendrite-free and high-performance aqueous zinc-ion batteries

As an emerging electrochemical device, aqueous zinc-ion batteries (ZIBs) present promising potential in safe and large-scale energy storage. However, the large pores of commercial glass fiber (GF) separators result in uneven Zn2+ ion flux, leading to severe dendrite growth issues of Zn metal anodes. Herein, we integrated a multifunctional layer on the GF separator that can synergistically regulate the pore feature and surface property of commercial GF separators. Such modification layer, composed of nanocellulose and SiO2 nanoparticles, exhibited uniform nanoporous structure and abundant negatively charged polar functional groups. These features allow regulating the distribution of Zn2+ ions at the separator-anode interface, facilitating stable and uniform Zn nucleation and growth. Moreover, the electrostatic interaction between the negatively charged functional groups and Zn2+ ions enhanced the Zn2+ ion transport kinetics, preventing the Zn dendrites formation and adverse reactions. Consequently, the modified electrolyte-filled GF separator showed an increased Zn2+ ion transference number of 0.65. The symmetric Zn//Zn batteries utilizing such a separator achieved an impressive cycling life of 500 h at a high current density/capacity of 10 mA cm-2/4 mAh cm-2, nearly nine times longer than the battery using the unmodified GF separator (<55 h). The superior electrochemical performance was verified in both Zn//AC and Zn//LiMn2O4 full battery evaluations. This work presents a novel synergistic modification strategy for developing advanced separators for aqueous ZIBs.

Patterned separator membranes with pillar surface microstructures for improved battery performance

In order to improve battery performance by tuning battery separator membranes, this work reports on porous poly(vinylidene fluoride-co-trifluoroethylene) - P(VDF-TrFE)- membranes with surface pillar microstructures. Separators with tailored pillar diameter, height and bulk thickness were fabricated by template patterning and computer simulations, allowing to evaluate the effect of the pillar microstructure characteristics on battery performance. It is shown that the different pillar microstructures of the separators affect the uptake value (150-325%), ionic conductivity value (0.8-1.6 mS·cm^-1) and discharge capacity of the lithium ion batteries (LIB) when compared with the separator without pillars. The experimental charge-discharge behavior demonstrates that the pillar parameters affect battery performance and the best microstructure leading to 80 mAh·g^-1 at 2C. Battery performance can be thus optimized by adjusting pillar diameter, height and bulk thickness of the separators keeping its volume constant, as demonstrated also by the simulation results. The parameter with most influence in battery performance is the bulk thickness of the separator, allowing to obtain a maximum discharge capacity value of 117.8 mAh·g^-1 at 90C for a thickness of 0.01 mm. Thus, this work shows that the optimization of the pillar microstructure of the separator membranes allows increasing the capacity towards a new generation of high-performance LIBs.