物理化学学报 >> 2019, Vol. 35 >> Issue (7): 755-765.doi: 10.3866/PKU.WHXB201810009

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基于室温离子液体的活化石墨烯粉末超级电容储能性能

杨康,帅骁睿,杨化超*(),严建华,岑可法   

  • 收稿日期:2018-10-08 发布日期:2018-12-21
  • 通讯作者: 杨化超 E-mail:huachao@zju.edu.cn
  • 基金资助:
    国家自然科学基金(51306159);浙江省自然科学基金(LR17E060002);中央高校基本科研业务费专项资金(2018XZZX002-17)

Electrochemical Performance of Activated Graphene Powder Supercapacitors Using a Room Temperature Ionic Liquid Electrolyte

Kang YANG,Xiaorui SHUAI,Huachao YANG*(),Jianhua YAN,Kefa CEN   

  • Received:2018-10-08 Published:2018-12-21
  • Contact: Huachao YANG E-mail:huachao@zju.edu.cn
  • Supported by:
    the National Natural Science Foundation of China(51306159);the Zhejiang Provincial Natural Science Foundation, China(LR17E060002);the Fundamental Research Funds for the Central Universities, China(2018XZZX002-17)

摘要:

室温离子液体(RTILs)具有电压窗口高等优点,被认为是实现超级电容高性能储能的绿色电解液。但是,离子液体的电导率低、粘度高,使得其储能性能不佳。本文探究了溶剂效应对离子液体超级电容储能性能的影响。以石墨烯粉末为活性材料,选取1-丁基-3-甲基咪唑四氟硼酸盐为离子液体,通过添加乙腈溶剂配置了具有不同摩尔分数ρIL的电解液(从0.25到1.0)。结果表明,溶剂效应对超级电容性能的影响与电压扫描速率或电流密度密切相关。低扫描速率下,溶剂对储能基本没有影响,而高扫描速率下,添加溶剂可显著提升比电容(在ρIL = 0.25时,增加~2倍)。这是由于溶剂削弱了离子-离子间交互作用,从而降低了电解液粘度(~29倍),内阻(~5.5倍)和介电弛豫时间(~6.3倍)。在ρIL = 0.25时,超级电容最大能量和功率密度分别为65.2 Wh·kg-1和18066.6 W·kg-1,显著优于近期文献报道结果。特别地,当工作温度提升到50 ℃时,其能量密度将达到85.5 Wh·kg-1,显著高于传统水系、有机电解液超级电容和铅酸电池,与镍金属氢化物和锂离子电池性能相当。

关键词: 超级电容, 室温离子液体, 溶剂效应, 电化学性能, 活化石墨烯粉末

Abstract:

Supercapacitors, advanced electrochemical devices, have attracted great interest due to their extraordinary properties, such as high power density, fast charging or discharging rate, and ultra-long cycle life. Currently, great efforts have been devoted to increasing their moderate energy density (typically < 5 Wh·kg-1). Especially, room temperature ionic liquids (RTILs) have been considered as a promising electrolyte for further improving supercapacitor's performances owing to their large voltage window, high thermal stability, and wide working temperature range. However, RTILs suffer from the high viscosity and poor conductivity stemming from their strong cation–anion interactions. In this work, we investigate the influences of solvent on the capacitive performance within RTIL-based supercapacitors. Activated graphene powders are employed as the electrode active materials, and 1-butyl-3-methyl-imidazolium tetrafluoroborate (BMIMBF4) is chosen as the electrolyte because of the wide applications in electrochemical energy storage. The mole fraction of BMIMBF4 (ρIL) in electrolytes can be regulated with adjusting the ratio of acetonitrile solvents (AN). Electrochemical measurements suggest that the solvent effects on the charge storage capability of supercapacitors depend strongly on the applied scan rate or current density. Specifically, at a lower scan rate of 10 mV·s-1, solvent exhibits a negligible influence on the electrochemical performance; however, at an elevated scan rate of 200 mV·s-1, solvent addition could prominently enhance the capacitance by ~2 folds. These results can resolve the controversial solvent effects reported in previous simulation and experimental studies. To interpret the as-obtained results, we further explore the solvent effects on the dynamic properties of electrolytes. It is found that solvent can effectively reduce the strong ion–ion interactions within pristine RTILs, thus decreasing the viscosity by ~29 times. Further electrical impedance spectroscopy tests suggest that the addition of solvent is able to significantly suppress the series resistance (by ~5.5 times) and dielectric relaxation time (by ~6.3 times), which thereby improves the rate capability of supercapacitors. We demonstrate that the maximum specific energy and power density of supercapacitor (ρIL = 0.25) are calculated to be 65.2 Wh·kg-1 at 1 A·g-1 and 18066.6 W·kg-1 at 20 A·g-1, respectively, among the best performances in the state-of-art literatures. More importantly, under an elevated working temperature of 50, its energy density can reach up to 85.5 Wh·kg-1 at 1 A·g-1, which is much higher than that of aqueous or organic solution based supercapacitors (< 10 Wh·kg-1) and lead-acid battery (20–35 Wh·kg-1), comparable to that of Ni metal hydride (40–100 Wh·kg-1) and lithium-ion battery (80–150 Wh·kg-1).

Key words: Supercapacitor, Room temperature ionic liquid, Solvent effect, Electrochemical performance, Activated graphene powder

MSC2000: 

  • O646