醚基电解液体系改善硬碳低温储钾性能研究

Ether-based electrolyte system to improve the potassiumstorage performance of hard carbon at low temperatures

由于钾离子斯托克斯半径小、溶剂配位能力低,钾离子电池(PIBs)在低温储能方面具有广阔的应用前景.然而,由于当前缺乏具有实用兼容性的电解液,PIBs的低温性能尚有待进一步提升与优化.硬碳(HC)具有无序结构多、层间间距大的特点,是最常用的钾离子电池负极材料.本文研究了室温(25℃)和低温(-20℃)条件下HC在不同电解液中的储钾性能,分析了电解质浓度和溶剂类型对PIBs低温性能的影响.研究发现,乙二醇二甲醚(DME)基电解液能优化钾离子溶剂化结构,改善电极表面固体电解质界面膜(SEI膜)的稳定性,从而提升HC的储钾性能.此外,电解质浓度也会显著影响HC的电化学性能.在制备的浓度为1 mol/L的六氟磷酸钾(KFP_(6))溶解于DME的电解液体系中,HC展现出了最优异的储钾性能.在25℃条件下,经过0.3 A/g电流密度下的100次充放电循环后,HC材料仍能维持高达163 mA·h/g的比容量.即使在-20℃低温条件下,在该电解液中HC初始放电比容量依然高达为280 mA·h/g,低温和常温性能明显优于常用的以碳酸乙烯酯(EC)和碳酸二甲酯(DMC)为溶剂的电解液.本工作对PIBs电解液的设计优化和低温性能改进具有重要的参考价值.

Potassium-ion batteries(PIBs)are promising for low-temperature energy storage due to the small Stokes radius of potassium ions and low solvent coordination ability.However,the performance of PIBs at low temperatures is poor due to the lack of suitable anode materials and electrolytes.Hard carbon(HC)is the most commonly used anode material for PIBs due to its many disordered structures and large interlayer spacing.In this paper,we studied the potassium storage performance of HC in different electrolytes at room temperature(25℃)and low temperature(-20℃)to analyze the effects of electrolyte concentration and solvent type on the low temperature performance of PIBs.It was found that the DME-based electrolyte could optimize the solvation structure of potassium ions and improve the stability of the SEI film on the electrode surface,thus enhancing the potassium storage performance of HC.In addition,the electrolyte concentration significantly affected the electrochemical performance of HC,which had the best potassium storage performance in the prepared DME electrolyte with a potassium hexafluorophosphate(KFP_(6))concentration of 1 mol/L,and still had a specific capacity of 163 mA·h/g after 100 cycles at 25℃at a current density of 0.3 A/g.Even at a low temperature of-20℃,the initial discharge specific capacity of HC in this electrolyte was still as high as 280 mA·h/g,which was significantly better than the commonly used BASE electrolyte with EC and DMC as solvents at both low and room temperatures.This work is informative for the design and low-temperature performance improvement of electrolytes for PIBs.