A novel imidazolium-based small molecule matching with unique solvation structure electrolyte for superior K-storage stability

Organic anodes for K-storage have attracted much attention because of high theoretical capacity, low cost and extensive natural resource although facing serious dissolving issues with conventional electrolytes and persistent capacity decay. Therefore, 2-methylimidazole (mIm), an imidazolium-based small molecule restricted with high electronic conductivity carbon nanotubes (mIm/CNTs) is applied for potassium-ion batteries (PIBs). Furthermore, this as-prepared anode is accompanied to the potassium bis(fluorosulfonyl)imide (KFSI)-ethylene carbonate (EC) and diethyl carbonate (DEC) electrolytes (KFSI/EC + DEC) with modifiable solvation structures. At current density of 50 mA g−1, the mIm/CNTs composite coupled with the optimized 3 mol L−1 KFSI/EC + DEC electrolyte provides an average reversible capacity of 240 mAh g−1 (composites) with coulombic efficiency (CE) of 99.5 %. After 500 cycles, a high sustained capacity of 200 mAh g−1 (composites) is attained at 200 mA g−1. This enhanced K-storage performance of mIm/CNTs in 3 mol L−1 KFSI/EC + DEC electrolyte can be attributed to distinctive solvation structure, which is dominated by contact ion pairs (CIPs) and aggregates (AGGs). This structure intensively mitigates dissolution issues and greatly promotes K+ reaction kinetics. This work emphasizes the significance of electrolyte regulation for organic anodes and will supply a comprehensive appreciating of electrochemistry performance for advanced energy storage systems. A novel mIm/CNTs anode, fabricated via restricting mIm with high electronic conductivity carbon nanotubes (CNTs), exhibited a high average reversible capacity of 240 mAh g−1 (composites) at 50 mA g−1 with a high coulombic efficiency (CE) up to 99.5 %, and maintained 200 mAh g−1 (composites) after 500 cycles at 200 mA g−1 (99.3 % of CE) in 3 M KFSI/EC + DEC electrolyte, demonstrating the superior electrochemical performance with enhanced capacity and cycle life when compared with previous organic anode potassium-ion batteries. [Display omitted] •A novel imidazolium-based molecule is proposed as K-storage anode.•An optimized ester-based electrolyte is matched with the organic anode.•Superior capacity of 240 mAh g−1 after 200 cycles at 50 mA g−1 is achieved.•Enhanced properties are attributed to electrolyte regulation.