Rational Design of Cellulose Nanofibrils Separator for Sodium-Ion Batteries

A Sodiophilic Amyloid Fibril Modified Separator for Dendrite-Free Sodium-Metal Batteries

Sodium (Na) batteries are being considered as prospective candidates for the next generation of secondary batteries in contrast to lithium-based batteries, due to their high raw-material abundance, low cost, and sustainability. However, the unfavorable growth of Na-metal deposition and severe interfacial reactions have prevented their large-scale applications. Here, a vacuum filtration strategy, through amyloid-fibril-modified glass-fiber separators, is proposed to address these issues. The modified symmetric cell can be cycled for 1800 h, surpassing the performance of previously reported Na-based electrodes under an ester-based electrolyte. Moreover, the Na/Na3 V2 (PO4 )3 full cell with a sodiophilic amyloid-fibril-modified separator exhibits a capacity retention of 87.13% even after 1000 cycles. Both the experimental and the theoretical results show that the sodiophilic amyloid fibril homogenizes the electric field and Na-ion concentration, fundamentally inhibiting dendrite formation. Simultaneously, the glutamine amino acids in the amyloid fibril have the highest adsorption energy for Na, resulting in the formation of a stable Na3 N- and NaNx Oy -rich solid-electrolyte-interface film on the anode during cycling. This work provides not only a possible pathway to solve the dendrite problem in metal batteries using environmentally friendly biomacromolecular materials, but also a new direction for expanding biomaterial applications.

Electrospun Sandwich-like Structure of PVDF-HFP/Cellulose/PVDF-HFP Membrane for Lithium-Ion Batteries

Cellulose membranes have eco-friendly, renewable, and cost-effective features, but they lack satisfactory cycle stability as a sustainable separator for batteries. In this study, a two-step method was employed to prepare a sandwich-like composite membrane of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP)/cellulose/ PVDF-HFP (PCP). The method involved first dissolving and regenerating a cellulose membrane and then electrospinning PVDF-HFP on its surface. The resulting PCP composite membrane exhibits excellent properties such as high porosity (60.71%), good tensile strength (4.8 MPa), and thermal stability up to 160 °C. It also has exceptional electrolyte uptake properties (710.81 wt.%), low interfacial resistance (241.39 Ω), and high ionic conductivity (0.73 mS/cm) compared to commercial polypropylene (PP) separators (1121.4 Ω and 0.26 mS/cm). Additionally, the rate capability (163.2 mAh/g) and cycling performance (98.11% after 100 cycles at 0.5 C) of the PCP composite membrane are superior to those of PP separators. These results demonstrate that the PCP composite membrane has potential as a promising separator for high-powered, secure lithium-ion batteries.