1Mie University, Japan; 2The Kansai Electric Power Co., Inc., Japan
There is a demand for developing a new battery system with higher energy density than conventional lithium ion batteries. Many of the researches have focused on the application of lithium metal anode, as it is an ideal anode material having low electrode potential and high specific capacity. However, lots of challenges must be overcome, for instance, its dendritic growth in the plating process has been a serious issue from a viewpoint of safety and energy efficiency.
In the electrochemical potential region lithium metal operates at, electrolyte materials are usually reductively decomposed and form a film called solid electrolyte interphase (SEI) on lithium metal electrode. Inhomogeneity in the film thickness and chemical nature results in non-uniform current distribution in the region close to the surface of the electrode. Therefore, thin and homogeneous SEI is essential to achieve uniform lithium metal plating and avoid formation of the dendrites.
In this work, several additives with inert tetrabutylammonium (TBA) cation were examined to stabilize the SEI on lithium metal. TBANO3 was found effective to improve coulombic efficiency regardless of the solvents, while TBAPF6 did not improve the efficiency for solvents examined. TBANO3 addition resulted in higher coulombic efficiency compared to the additive-free one. In a given condition, average coulombic efficiency and short-circuit time was largely improved with the nitrate added electrolyte. The results indicate that anion plays more important role in SEI formation. To discuss the effect of anion in detail, surface of the lithium metal treated in the presence of these anions was examined by XPS analysis. In this presentation, the relationship between SEI compositions and electrochemical performances of lithium metal anode will be discussed.
11:00am - 11:30am Invited
Recent Progress on Cathode Design for High-Performance Li-Air Batteries
CAS Key Laboratory of Materials for Energy Conversion, Shanghai Institute of Ceramics, Chinese Academy of Sciences, China
Li(Na)-O2 battery is a fascinating energy storage technology because of its ultrahigh gravimetric energy density approaching that of gasoline, which is desirable for long-range electric vehicles. However, the Li-O2 batteries still face many problems, including the high charge overpotential, low energy efficiency and poor cycle performance. These problems are mainly attributed to the low-efficiency reversible formation of the Li2O2 discharge products. Therefore, in the course of the last decade, great efforts have been devoted to designing and synthesizing highly-efficiency cathode for Li-O2 batteries.
Our group has been concentrating on designing novel structure and exploring efficient catalysts of the cathode to get enhanced performance. Specifically, free-standing structural catalysts with nanowire and wave-like morphology are found to be efficient on reducing the overpotential. These pure electrodes without additional carbon and binder materials show excellent reversibility during discharge and charge process. By developing hydrophilic cathode, the air-liquid-solid interface can be greatly improved to facilitate fast oxygen diffusion, leading to enhanced performance. Furthermore, multi-phase metal oxides composites and materials structural modulation also demonstrate greatly enhanced catalytic performance. Moreover, insights of the electrocatalytic mechanism, especially for the metal oxide catalysts, are also obtained. In this presentation, the perspective of Li(Na) oxygen batteries will also be discussed.
11:30am - 11:45am Oral
A Free-Standing Zn-air Battery Air Electrode Based on Vertically Alighed Carbon Nanotubes on Graphene Foam
1Nanyang Technological University, Singapore; 2Nanjing Tech University, China
Zn-air batteries are being considered for many applications because of their high energy densities and low cost. the development of an effective air electrode for oxygen reduction reaction remains a challenge. We report the synthesis of free-standing structure of vertically aligned carbon nanotubes (VACNTs) supported by graphene foam, which were doped and loaded with iron-cobalt bimetallic catalyst and used as an air cathode. We have demonstrated that the iron-cobalt bimetallic catalyst is an excellent catalyst for oxygen reduction reaction, and the structure of the air electrode is also favorable for Zn-air batteries. Due to the low solubility and diffusivity of oxygen in the electrolyte, oxygen reduction in Zn-air batteries are designed to take place in tri-phrase interfaces in which the catalyst, electrode and air come in contact. The free-standing electrode has a well-engineered hierarchical structure which contains both larger pores that acts as highways for oxygen diffusion and mesopores that increases the surface area and creates more three-phrase interfaces for the reaction. The VACNT-graphene foam structure also processes excellent electrical conductivity. It bypasses the high PTFE content (typically about 30%) in conventional electrode preparation, which severely hinders the electric conductivity of the electrode, reducing battery performance and preventing the development of Zn-air batteries in high power density. Overall, this electrode demonstrates excellent electrochemical oxygen reduction reaction (ORR) activity. Zn-air battery assembled by this free-standing electrode shows higher performance than commercial Pt/carbon black (Pt/C) electrocatalyst prepared similarly. Rechargeable Zn-air batteries are also achieved with the free-standing electrode with a cycle life significantly higher than conventional electrodes.
11:45am - 12:00pm Oral
An Inorganic Electrolyte Based Molten-Air Battery With Improved Performance
Guruprakash KARKERA, A.S. PRAKASH
CSIR-Central Electrochemical Research Institute-Chennai unit, India
Li-air batteries gained enormous interest in last few years for their attractive theoretical energy density compared to state-of-the-art Li-ion batteries. However, low rate performance, deteriorated cycle life and energy inefficiencies hinder the progress and adoptability. Performance of non-aqueous Li-air batteries are retarded due to adverse reactions associated with non-aqueous electrolytes. As an alternative to unstable non-aqueous electrolytes generally used in Li-air batteries, inorganic metal salts are investigated as molten electrolytes at intermediate temperature. Present study investigates the use of LiNO3-KNO2-CsNO3 (37-39-24) eutectic salt mixtures at 140 °C as electrolyte, lithium as anode and vulcan carbon as cathode to demonstrate improved cycle life and energy efficient molten Li-air battery. X-ray diffraction and FESEM studies are used to show that Li2Ox is reversibly formed during cycling with a charge-discharge overpotential of 0.3 V after 100 cycles (limited capacity of 500 mAhgcarbon-1). Improved cyclability is attributed to better solubility of discharge product at preeminent temperature and the reduced cell resistance due to high ionic conductivity of molten electrolyte. Operating the Li-air battery in molten electrolytes at elevated temperature could open a new window for solving adverse problems associated with electrolytes.