Multifunctional sulfate-assistant synthesis of seaweed-like N,S-doped carbons as high-performance anodes for K-ion capacitors

Abstract

K-ion capacitors (KICs) have gained wide attention as next-generation energy storage devices due to high power and long lifetime, as well as the low cost of K. Porous carbons with open structures and heteroatom doping are promising candidates for high-performance anode materials of KICs. Unfortunately, the synthesis methods of these porous carbons are commonly less efficient and unsustainable. In this work, a seaweed-like porous carbon with N/S heteroatoms is prepared using fish scale as the precursor. Different from previous work, K₂SO₄ is used as a triple-functional auxiliary (activator, template, and dopant), realizing the direct synthesis of N,S-doped porous carbon (referred to as NSPC700). NSPC700 is further used as an anode for KIC and its energy storage mechanism is systematically studied and revealed by in situ and ex situ characterization. It is revealed that specific N/S heteroatom doping and unique open structure endow the NSPC700 anode with high reversible capacity (462 mA h g⁻¹ at 0.05 A g⁻¹), good rate capability, and long cycling stability. Consequently, the assembled KIC delivers a high energy density of 129 W h kg⁻¹, high power density of 2.3 kW kg⁻¹, and long lifetime (88% capacity retention after 12 000 cycles).