Cycling Performances of Lithium-Air Cells Assembled with Mixed Electrolytes of Ionic Liquid and Diethylene Glycol Diethyl Ether

Abstract

Ionic liquid-based electrolytes composed of diethylene glycol diethyl ether (DEGDEE) and 1-butyl-1-methyl pyrrolidinium bis(trifluoromethane) sulfonyl imide (BMP-TFSI) were prepared and evaluated for non-aqueous lithium-air cell applications. Adding an appropriate amount of BMP-TFSI to the electrolyte solution improved ionic conductivity, oxidative stability and interfacial stability, and reduced flammability and volatility. When BMP-TFSI was mixed with DEGDEE under optimal condition, the cycle performance was remarkably improved as compared with either the organic electrolyte or ionic liquid electrolyte alone. The Li-air cell assembled with an optimized ionic liquid-based mixed electrolyte initially delivered a high discharge capacity of 10,620 mAh g −1 and exhibited good cycling stability exceeding 150 cycles at a current density of 0.1 mA cm −2 by limiting depth of discharge to 500 mAh g − Rechargeable Li-air batteries using oxygen in the air have attracted great interest as a potential power source due to their high theoretical specific energy of 11,000 Wh kg −1 , which is close to that of conventional gas-powered engines.1-8 The non-aqueous Li-air battery usually consists of a lithium negative electrode, an organic electrolyte and a porous carbon positive electrode. The successful development of Li-air batteries depends on these components having long-term stability and highly reversible formation and decomposition of Li 2 O 2 as a desired discharge product.6,9-11 The electrolyte presents one of the greatest challenges to practically exploiting Li-air batteries. Initially, alkyl carbonate-based electrolytes, such as propylene carbonate, were widely studied; however, they are susceptible to nucleophilic attack by oxygen reduction species.12-14 Ether-based electrolytes, such as tetra(ethylene glycol) dimethyl ether (TEGDME), are known to be more stable than alkyl carbonates. [15][16][17][18] Although TEGDME has been identified as a relatively stable electrolyte against nucleophilic attack, the repeated cycling caused irreversible chemical changes in the electrolyte, which resulted in formation of decomposition products such as Li 2 CO 3 , HCO 2 Li, CH 3 CO 2 Li, CO 2 and H 2 O. To overcome the irreversibility caused by attack of superoxide anion radical (O 2•− ), our group investigated a diethylene glycol diethyl ether (DEGDEE)-based electrolyte. The Li-air cell with a DEGDEE-based electrolyte exhibited a fairly stable cycling behavior when compared with that of a TEGDME-based Li-air cell.19 Nevertheless, the cycling stability was still not satisfactory due to electrolyte instability caused by its volatile nature and parasitic reactions between the organic electrolyte and the oxygen reduction species. As an alternative electrolyte, ionic liquids can be promising candidate because they have negligible vapor pressure, are non-flammable and have high electrochemical stability. [20][21][22] Moreover, ionic liquids can effectively interact with superoxide anion radicals and thus mitigate radical attacks during cyc...

Electrochemical Properties of Large-Discharge-Capacity Air Electrodes with Nickel Foam Sheet Support for Lithium Air Secondary Batteries

“…Therefore, the thickness of the nickel foam sheet was regarded as the thickness of the air electrode. The loading of 17 mg/cm 2 was notably high even though the air-electrode in this study was much thicker than the ones in previous reports focusing on the areal capacities, [36][37][38] which indicated the use of a nickel foam sheet was effective for obtaining high-loading air electrodes. Figure 1 shows discharge curves of LAB cells incorporating air electrodes prepared thus.…”

“…Furthermore, it is necessary to evaluate areal discharge/charge capacities to increase practical battery energy density. Recently, some trials [36][37][38] have been reported with a similar view. Y. Lin et al reported holey-graphenebased air electrodes with high loading of up to 10 mg/cm 2 .…”

Lithium–oxygen batteries with ester-functionalized ionic liquid-based electrolytes

“…A low salt concentration was used to prepare the mixed electrolytes, as higher amounts of salt increased the viscosity, which in turn reduced the ionic conductivity due to an increase in ionic interactions within the solution. 30,33 The contents of ionic liquid in the mixed solutions were 0, 25, 50, 75 and 100% based on volume. The mixed electrolyte systems will be abbreviated as IMI-N, PYR-N, PIP-N, and MOR-N, where N is the volumetric percent of ionic liquid in the mixed electrolyte solutions, and IMI, PYR, PIP and MOR represent type of ionic liquids, i.e., MMEsIm-TFSI, MEEsPyr-TFSI, MEEsPip-TFSI, and MEEsMor-TFSI, respectively.…”

“…27,28 Recently, it has been demonstrated that mixed electrolytes composed of organic solvent and ionic liquid could overcome the drawbacks associated with the individual components by combining the useful properties of each constituent. 26,[29][30][31] However, research into ionic liquid-based mixed electrolytes for lithium-oxygen batteries is at an early stage and thus, the studies on mixed electrolytes employing new ionic liquids with different structures deserve to be carried out.…”

A bi-functional metal-free catalyst composed of dual-doped graphene and mesoporous carbon for rechargeable lithium–oxygen batteries

“…36,37 All cells and electrolytes were prepared in an argon-lled glovebox with H 2 O and O 2 contents less than 1 ppm. The organic electrolyte was 1 M lithium bis(triuoromethane) sulfonylimide (LiTFSI) dissolved in tetra(ethylene glycol) dimethyl ether (TEGDME).…”