Lithium electrochemistry and cycling behaviour of ionic liquids using cyano based anions

Abstract

Lithium based battery technologies are increasingly being considered for large-scale energy storage applications such as grid storage associated with wind and solar power installations. Safety and cost are very significant factors in these large scale devices. Ionic liquid (IL) electrolytes that are inherently nonvolatile and non-flammable offer a safer alternative to mainstream lithium battery electrolytes, which are typically based on volatile and flammable organic carbonates. Hence, in recent years there have been many investigations of ionic liquid electrolytes in lithium batteries with some highly promising results to date, however in most cases cost of the anion remains a significant impediment to widespread application. Amongst the various possible combinations the dicyanamide (DCA) anion based ionic liquids offer exceptionally low viscosities and high conductivitieshighly desirable characteristics for Li electrolyte solvents. DCA ILs can be manufactured relatively inexpensively because DCA is already a commodity anion, containing only carbon and nitrogen, which is produced in large amounts for the pharmaceutical industry. In this study we use the non-fluorinated ionic liquid N-methyl-N-butylpyrrolidinium dicyanamide to form non-volatile lithium battery electrolytes. We demonstrate good capacity retention for lithium metal and LiFePO 4 in such electrolytes and discharge capacities above 130 mAh.g À1 at 50 C. We show that it is important to control moisture contents in this electrolyte system in order to reduce capacity fade and rationalise this observation using cyclic voltammetry and lithium symmetrical cell cycling. Having approximately 200 ppm of moisture content produces the optimum cycling ability. We also describe plastic crystal solid state electrolytes based on the DCA anion in the lithium metal-LiFePO 4 battery configuration and demonstrate over 150 mAh.g À1 discharge capacity without any significant capacity fading at 80 C. Broader context Lithium battery technologies have applications in large-scale energy storage such as grid storage and electric vehicles. Safety, energy density, and cost are very crucial factors in the choice of large scale devices. Currently, mainstream lithium-ion battery electrolytes are based on volatile and ammable organic carbonates which introduce signicant safety issues. Ionic liquid (IL) electrolytes, which are inherently non-volatile and non-ammable, offer a safer alternative. Additionally, ILs offer the promise of enabling a rechargeable lithium metal electrode to deliver signicant increases in energy. Amongst the various possible cation and anion combinations, ILs using the dicyanamide (DCA) anion, which contain no uorine reducing cost, offer exceptionally low viscosities and high conductivitieshighly desirable characteristics for Li electrolyte solvents. We have investigated the ionic liquid N-methyl-N-butylpyrrolidinium dicyanamide to form lithium battery electrolytes which enable good capacity retention for a lithium metal-LiFePO 4 battery with discharge ca...

TiO2-based ionogel electrolytes for lithium metal batteries

“…2(c), is also an important electrochemical property. It can be seen that there is no signs of remarkable random fluctuations, as well as sudden voltage drop with ongoing cycling, suggesting a stable SEI film formed on lithium metal, and no short-circuiting phenomenon [3,16], which proves that the TIE is capable of promoting uniform lithium electrodeposition and limiting lithium dendrite proliferation. These results indicate that the as-prepared TIE could be applied as a promising candidate in LMBs.…”

Development of Electrolytes towards Achieving Safe and High‐Performance Energy‐Storage Devices: A Review

“…[133][134][135][136][137][138][139][140][141][142][143][144][145] They can be employed either directly as the electrolyte, for example in supercapacitors, or as the solvent for ionic liquid electrolytes (ILEs). [133][134][135][136][137][138][139][140][141][142][143][144][145] They can be employed either directly as the electrolyte, for example in supercapacitors, or as the solvent for ionic liquid electrolytes (ILEs).…”

Ionic‐Liquid‐Based Polymer Electrolytes for Battery Applications

“…[5] In other contexts,s uch as as earch for environmentally benign extraction or reaction media, many fluorine-free ILs have been synthesized and characterized, but not with regard to their electrochemical stability. However,i tc an be expected that their cost will drop significantly once their production has surpassed ac ertain level.…”