Crab shell derived chitin nanofiber separator for high-rate potassium-ion batteries

Abstract

Potassium-ion batteries (PIBs) are promising alternatives to lithium-ion batteries (LIBs) due to its cost-effectiveness, high voltage, and compatibility with aluminum collectors. However, challenges such as uneven potassium deposition and rapid capacity decay, especially at high current densities, hinder its development. Separators play a key role in the performance of batteries. Conventional glass fiber (GF) separators exhibit poor wettability and uneven pore sizes, accelerating polarization. Recent advances in separator engineering, including coated GF or Polyolefin (PP) functional separators, face limitations such as functional layer depletion or delamination. Herein, a partially deacetylated chitin nanofibers (PDC) separator was developed via hydrothermal treatment and filtration. The rich -NH₂ groups of PDC separator immobilized anions in electrolyte through hydrogen bond between H from -NH2 groups and anions, thus dissociating potassium salt thus improving K+ transference number (t_(K^+ )). The immobilization of anions also contributes to the interface stability between electrolyte and electrode. Besides, the uniform nanofibers obtained by filtration formed uniform nanopores of PDC separator, promoting smooth potassium deposition. The as-prepared PDC separator obtained a high t_(K^+ ) of 0.54. The Graphite||K cell with PDC separator achieved a discharge capacity of 203 mAh g-¹ at 200 mA g-¹, 236% of that with GF separator. The high-rate performance stems from accelerated K⁺ transport and improved interface stability. This work highlights the potential of chemically tailored natural polymer nanofibers as high-performance separators for PIBs, offering a sustainable and scalable strategy for next-generation energy storage.