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 their 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 their 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 (PDC) nanofiber separator was developed via hydrothermal treatment and filtration. The rich –NH₂ groups of the PDC separator immobilized anions in the electrolyte through a hydrogen bond between H from –NH₂ groups and anions, thus dissociating potassium salt and improving K⁺ transference number (t_K⁺). The immobilization of anions also contributed to the interface stability between the electrolyte and the electrode. Besides, the uniform nanofibers obtained by filtration formed uniform nanopores in the PDC separator, promoting smooth potassium deposition. The as-prepared PDC separator obtained a high t_K⁺ of 0.54. The graphite||K cell with the PDC separator achieved a discharge capacity of 203 mAh g⁻¹ at 200 mA g⁻¹, which is 236% of that with the GF separator. The high-rate performance stemmed from the 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.