Dual-salt assisted synergistic synthesis of Prussian white cathode towards high-capacity and long cycle potassium ion battery

Prussian blue analogues(PBAs) are considered as superior cathode materials for potassium-ion batteries(PIBs) because of their three-dimensional open framework structure,high stability,and low cost.However,the intrinsic lattice defects and low potassium content typically results in poor rate and cycling performance,thus limited their practical applications.In this work,high-quality K1.64FeFe(CN)6(PW-HQ)material with less crystalline water(6.21%) and high potassium content(1.64 mol^(-1)) was successfully synthesized by a novel coprecipitation method with potassium citrate(K-CA) and potassium chloride(KCl) addition.Specifically,the electrode delivers a reversible capacity of 113.1 mA h g^(-1)at the current rate of 50 mA g^(-1)with~100% coulombic efficiency.Besides,the electrode retained 90% reversible capacity at 500 mA g^(-1)current density after 1000 cycles,indicating only 0.01% capacity decay per cycle.Moreover,we have revealed that the introduction of K-CA controlled the chelating rate of Fe(Ⅱ) and the addition of KCl increased the K+content,hence improving the capacity and stability of the asprepared electrodes.Structural evolution and potassium storage mechanism were further investigated by detailed ex-situ X-ray diffraction and in-situ Raman measurements,which demonstrated reversible potassiation/depotassiation behavior and negligible volume change during the electrochemical process.In general,this work provides an efficient strategy to eliminate water contents in Prussian blue cathode and improve its electrochemical performance,which plays a key role in promoting the industrialization of potassium ion batteries.

Nanopore design of sulfur doped hollow carbon nanospheres for superior potassium-ion battery anodes

Sulfur doped carbonaceous materials are promising anodes for potassium-ion batteries because of their ability to bridge active sites and induce C/S electron coupling,resulting in increased ion storage capacitance However,the large potassium ions could cause significant volume expansion and structure collapse during operation in sulfur doped carbonaceous anodes,which lead to rapidly capacity sacrifice during long-term cycling.Nanopore design for anchoring sulfur atom in carbon skeleton is a novel way to alleviate the structure collapse and maintain the cycling stability.Therefore,this study developed a controlled nanopore and sulfur doped carbon sphere structure(S-NPHCSs).In potassium-ion batteries S-NPHCSs anode demonstrated exceptional performance with a high reversible capacity of 247 mAh·g^(–1)after 50 cycles at 0.2 A·g^(–1)and delivered a long cycle stability of 600 cycles at a high current density of 1.0 A·g^(–1).Interconnected nanopores and doped sulfur structure not only expand the accumulation space and offer ample active sites for diffusion and adsorption of potassium ions,but also build stable channels through nanopore structure to ensure the cyclic stability.This finding provides a fundamental theory for designing nanopore structures and introducing sulfur doped carbonaceous materials to enhance capacitive potassium storage and long cycle stability.

Flash-assisted doping graphene for ultrafast potassium transport

Graphene has been widely used for electrical energy storage and its performances could be further improved by heteroatom doping.How to prepare doped graphene efficiently and economically remains a significant challenge.Here,we propose a flash-assisted doping method to produce nitrogen-and sulfur-doped graphene(N-rGO and S-rGO).Using this method,graphene oxide(GO)is reduced to few-layer graphene(rGO)in seconds without the use of reductants,accompanied with a high doping efficiency.Particularly,the as-synthesized N-rGO with a high N content of 12.75 at.%used as potassium-ion battery(KIB)anode exhibits ultrafast K+-transport kinetics and superior K^(+)-storage capability.Quantitative kinetics analysis and theoretical simulation are used to reveal the mechanism of transportation and storage of K^(+)in N-rGO.