Mild-Expanded Graphitic Onion-like Carbon with Nonflammable Electrolytes for Safety and High-Performance Potassium Storage

Thiswork provides an effective strategy for improving thesafety, high power, and wide operating temperature range of potassium-basedelectrochemical energy storage devices. Potassium-ion batteries (PIBs) are attractive energystorage devicesdue to the abundant low-cost potassium resources, and graphite isone of the most competing anodes of PIBs. Nevertheless, graphite oftensuffers from sluggish kinetics, large volume variations, and highactivity of K+, leading to poor rate and low-temperatureperformance, insufficient cyclability, and safety issues. Herein,mild-expanded graphitic onion-like carbon (MEGOC) with an enlargedinterlayer distance is prepared from confined graphitic onion-likecarbon by liquid-phase oxidation and slow thermal reduction, whichcan accommodate volume variations and promote potassium diffusion.Meanwhile, using triethyl phosphate, a nonflammable and low-melting-pointelectrolyte ensures safety and low-temperature operation performance.In the nonflammable potassium-ion electrolyte, MEGOC exhibits longcycle life at a high rate (175 mA h g(-1) at 2C after1500 cycles) and superior low-temperature performance (165 mA h g(-1) at -40 & DEG;C). Furthermore, an assemblednonflammable potassium-ion capacitor with MEGOC as the anode exhibitshigh reversibility and superior energy/power density at ambient andlow temperatures. Accordingly, combining structural engineering andelectrolyte engineering is an effective strategy for improving thesafety and high performance of potassium-based electrochemical energystorage devices.