Synthesis of Gel Polymer Electrolyte with Enhanced Oxygen Reduction Reaction for Lithium-Air Batteries

Lithium-air batteries have been focused for last several decades because of its high theoretical energy density such as 10⁴ Whkg^-1 [1]. Many researchers have researched to realize high practical capacity of lithium-air batteries and much higher practical energy density (over 4000mAhg^-1) than practical energy density of lithium ion batteries (~360 mAhg^-1) has been reported. In addition, development of diverse effective organic-based electrolyte leads to realize good cycleability. However, using liquid type organic electrolyte has many problems such as evaporation, contamination by water from the ambient air, leakage, safety hazard and flammability [2].

Applying gel polymer electrolyte as solid type electrolyte can be one strategy to solve the problems mentioned above. The poly vinylidene fluoride (PVDF) has good property to be used for solid electrolyte matrix such as high dielectric constant to dissolve the lithium salts, thermal stability and good mechanical property [3]. So that, some researches using PVDF electrolyte matrix for solid type electrolyte has been reported in battery society [3, 4]. However, in case of lithium-air batteries, the contact of interface between cathode and electrolyte is significant to drive chemical reaction due to the volume change of air cathode part by formation of lithium peroxides. Moreover, oxygen reduction reaction and oxygen evolution reaction processes must be smooth in the solid type electrolyte as in liquid type electrolyte.

In this work, we synthesize the morphology changeable PVDF matrix solid type electrolyte with LiTFSI/TEGDME, and characterize its mechanical and electro chemical characteristics. The electrolyte is synthesized using electro-spun technology and the polymer chain reaction control skill. In the middle layer of membrane, the textile structure composed of PVDF micro fibers leads to good mechanical property and it functions as separator. The soft electrolyte part as interface contacting with electrodes is synthesized by addition of benzoquinone as inhibitor to stop chain reaction of PVDF matrix. And the benzoquinone, also, leads to improve cycleability of the lithium-air batteries by enhancing ORR process. Enhancing ORR process accelerates formation of Li₂O₂ reaction products during discharge. We demonstrate that the ionic conductivity is up to 1 x 10^-3 Scm^-1by calculating of impedance analysis. Also, the synthesized electrolyte shows over 20 stable charge-discharge cycle characteristics.

Acknowledgment

This research was supported by the MSIP(Ministry of Science, ICT and Future Planning), Korea, under the “IT Consilience Creative Program” (NIPA-2014-H0201-14-1002) supervised by the NIPA(National IT Industry Promotion Agency)

[1] K. M. Abraham and Z. Jiang, J. Electrochem. Soc. 143 (1996)1.

[2] J. Christensen, P. Albertus, R. S. Sanchez-Carrera. T. Lohmann, B. Kozinsky, R. Liedtke, J. Ahmed and A. Kojic, J. Electrochem. Soc. R1 (2012) 159

[3] Y. Zhu, S. Xiao, Y. Shi, Y. Yang, Y. Hou and Y. Wu, Adv. Energy. Mater. 4 (2014) 1300647

[4] P. Yang, L. Liu, L. Li, J. Hou, Y. P. Xu, X. Ren, Electrochimica Acta 115 (2014) 454