Dong Joon Lee joined Battery Group of Samsung Advanced Institute of Technology (SAIT) as a research scientist in 2007. He received his B.S. (2000) and Ph.D. (2006) degrees in Department of Chemistry from Seoul National University, Korea. His PhD thesis focused on development of synthetic utilities of organic intermediates. He moved to School of Physics in Seoul National University in 2006 as a postdoctoral associate to work on patterning and massive assembly of nano-size materials on various surfaces and fabrications of devices.   His research experience covers organic chemistry, nano-material patterning, Li-ion battery, and lithium-air battery. His current activity is mainly on lithium-air battery.

Abstract

Lithium-sulfur and lithium-air batteries are attractive because they have the potential of providing 2 to 5 times the energy density of the lithium-ion batteries currently on the market. However, lithium-air batteries suffer from large polarization between charge and discharge and poor cycleability due to electrolyte decomposition and the high potential needed to remove lithium from Li2O. In the case of lithium-sulfur batteries, although progress has recently been made by fabrication of a carbon-sulfur composite [1,2], substantial improvements are still needed. The main challenge is the poor cycle life resulting from the dissolution of polysulfide in the organic electrolyte and its migration to the anode. Moreover, to overcome the insulator characteristic of sulfur (5 × 10−30 S/cm at 25 °C) and Li2S (final product of Li-S cell), special carbon (e.g., carbon mesopores [1]) or high amounts of carbon [2] are needed for high current density applications. Another drawback of lithium-sulfur batteries is that the voltage output is close to 1.8 V, and the cell cannot be cycled over 3.6 V.

In this paper, we report on a new battery system based on selenium and selenium-sulfur composite. Selenium has a melting point of 217 ºC and an electronic conductivity of 10-5 S cm-1, which is 20 orders of magnitude higher than that of sulfur because the gap between the valence band and the conduction band is reduced with decreasing atomic number. In earlier preliminary work, we investigated the electrochemical properties of selenium as a host for lithium ions. We found that this new class of electrodes can compete with the lithium-sulfur system in terms of energy density, even though the theoretical capacity of the Li /Se system based on the formation of Li2Se is only 675 mAh g-1, much lower than that of the Li/S system (1675 mA g-1). However, the high density of selenium (4.82 g/cm3) versus sulfur (2.07 g/cm3) makes the volumetric capacity of these materials very close (~3253 Ah/l for selenium and ~3467 Ah/l for sulfur). Furthermore, we found that the Li/Se system delivers an output voltage at least 0.5 V higher than that of Li/S and could surpass the Li/S system in terms of volumetric energy density. Furthermore, S-Se mixtures are miscible in all proportions and many selenium-sulfur composites including Se5S, Se5S2, Se5S4, SeS, Se3S5, SeS2 are already reported. Those known Se-S materials can offer higher theoretical capacities than the selenium alone ranging from 675-1550 mAh.g-1 with improved conductivity compared to pure sulfur. The potential Se-S systems will allow for tunable electrodes, combining the high capacities of S-rich systems with the high conductivity associated with the d-electron containing Se. Unlike Li/Sulfur system, both Se and SexSy can be cycled to 4.6V without failure. We will also report on new improvement in cycle life of lithium air using two ether-based electrolytes; tetraglyme (tetra (ethylene glycol) dimethyl ether. TEGDME) and a siloxane (tri(ethylene glycol) methyltrimethyl silane, 1NM3).

References

1.    J. Xiulei, T.L. Kyu, & L. F. Nazar, Nature Mater., 8, 500-506 (2009).
2.    B. Zhang, X. Qin, G.R. Li  & X.P. Gao, Energy Environ. Sci., 3, 1531–1537 (2010).

The lithium/sulfur battery has a high theoretical specific energy of 2600Wh/kg, which has been a strong incentive for next generation battery. However, it is difficult to obtain high utilization and long cycle life because of insulating nature of sulfur and solubility of lithium polysulfides in organic electrolytes. These problems could be overcome by optimization of sulfur electrode structure and electrolytes. In this presentation, I will review the previous approaches and report my recent results such as rate capability and cycling property using sulfur-carbon nanocomposite cathode and modified electrolytes.

Gas cleaning where specific substances are removed down to a very low level is required in many catalytic processes either to avoid deactivation of catalysts or for environmental reasons. One example is ammonia synthesis where all oxygen-containing molecules have to be removed from the synthesis gas since the ammonia synthesis catalyst otherwise will be severely poisoned. Another example is production of chemicals like e.g. methanol from synthesis gas obtained from gasification of coal or biomass; here thorough cleaning of the gas from a lot of substances like heavy metals, S, Cl, and NH3 is required.

The technologies usually used for gas cleaning are scrubbing with liquids or absorption by solids. The presentation will review the possibility to use similar technologies for full or partly removal of water and CO2 from air to be used in Li-air batteries. By simple assumptions it is evaluated how different methods and process designs will influence the energy densities of the Li-air battery on the system level.

Scientists across LBNL have come together to participate in a broad new program of research to help provide the basis for a sustainable energy future called, Carbon Cycle 2.0.  This includes efforts in climate modeling, energy analysis, building efficiency, combustion, batteries and energy storage, biofuels, carbon capture and sequestration, solar PV and artificial photosynthesis.

The program seeks to provide a common energy analysis component for all of these efforts, as well as links to scenario based climate models to help understand what the prospective impacts of each program could be.

The Li-O2 battery is generating a great deal of interest because theoretically it possesses a specific energy 5-10 times that of a conventional Li-ion battery. Very little is known about the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) in lithium-air battery cathodes based on aprotic organic electrolytes. A systematic study using both traditional RDE measurements as well as cell level measurements in conjunction with various characterization techniques will be presented. We begin by drawing analogies between the oxygen electrode reactions in the aqueous electrolyte, in particular alkaline electrolyte, and the aprotic (Li+ free) non-aqueous electrolytes. Employing extended surfaces of Au we will demonstrate that the ORR in these electrolytes is governed by the same principles that dictate the reaction mechanisms in protic solvents. We will also employ R(R)DE techniques to both quantitatively and qualitatively determine the reaction products namely the superoxide and peroxide. This will be used to determine the stability of the various ethers and carbonate solvents toward the superoxide species. Extending this study to Li+ based solvents will be used to further determine the products formed, their stability, their strength of adsorption to the electrode surface, and the measure of reversibilities achieved using RDE measurements. Furthermore, using an electrochemical voltammetric finger printing technique, we will aim to understand the nature of products formed in the presence of Li+ cations and the ease of their re-chargeability. Extending this approach to study carbonaceous materials will help us better delineate the role of morphology, nature of carbon and the relative geometry effects on observed reversibility of Li-O¬2 cathode interfaces. A careful study on the role of surface active groups and their impact on both the reduction and oxidation reactions will be studied both in a traditional three-electrode setup as well as our in-house design battery cell design (KF cell). The presence of side reactions that can occur at the cathode interfaces, particularly related to electrolyte oxidation will be discussed briefly. This will help us to understand the reaction that determines the observed charging plateaus. The KF cell then allows us to both determine the potentials at which gasses are generated/consumed using a pressure-change measurement, which can then in conjunction with DEMS be used to identify the nature of products formed during the charging process. Also, using the “expected products” in the battery directly we determine the expected voltages at which they can be oxidized and correlate them with the real battery charging potentials. This helps us to draw a conclusion regarding the nature of products formed during discharge and the potential charging reactions.

While Li-air battery has recently become one of the most actively studied power sources for future electric vehicles, its short cycle life still remain a hurdle in the development of practical batteries. Li dendrite formation and electrolyte decomposition are frequently discussed as main causes of cell failure. We constructed a nonaqueous Li-air cell with protected Li anode employing two different nonaqueous electrolytes on cathode and anode sides respectively. With carefully designed cycling conditions, the discharge and charge of the cell could be repeated more than 100 times without significant degradation of performance. A post-mortem analysis of the eventually failed cell was performed and the tasks for further improvement of the cycle life will be discussed in the presentation.

Aleksandar Kojic received his B.Sc. from the Mechanical Engineering Department of the University of Kragujevac, Serbia, and his M.S.M.E. and Ph.D. from the Mechanical Engineering Department at the Massachusetts Institute of Technology in Cambridge, in 1995, 1998, and 2001, respectively.  He is currently the head of the Energy Technologies Department at the Research and Technology Center of Robert Bosch LLC, Palo Alto, California.  His research interests are in the area of energy storage and conversion systems.

Among many challenges being addressed to develop practical Li air batteries, relatively little attention has been devoted to the effects of atmospheric contamination on the active cathode chemistry in Li air cells, as most researchers discharge cells under either pure oxygen or zero air.  Reaction of Li2O2, the dominant discharge product in nonaqueous Li-O2 cells, with certain atmospheric gasses could lead to formation of products which require high overpotentials to oxidize, leading to losses in both energy efficiency and cyclability.  Even in aqueous Li-O2 cells, CO2 contamination is a critical issue, as it reacts with the dominant discharge product, lithium hydroxide, to form sparingly soluble lithium carbonate, which dramatically reduces the capacity of the cell. Furthermore, the deleterious effects of O2, N2, H2O and CO2 on a cyclable lithium metal anode have been extensively explored. Clearly, if rechargeable Li-air batteries are to ever achieve a specific and volumetric energy density significantly higher than Li-ion batteries, novel, compact, energy efficient air purification technologies will need to be developed.  One such possible system could be membrane-based.

This presentation will outline the effects of three atmospheric gasses- nitrogen, carbon dioxide, and water- on the Li-O2 electrochemistry.  Afterwards, the viability of using a compact membrane system to separate N2, CO2, and H2O from O2, with the end goal of providing the highest purity O2 for a Li-O2 cell, will be discussed.

Li metal is studied as the anode materials for Li-ion and Li-S batteries, but protection of the reactive Li surface is a significant challenge. In this presentation, we will discuss new strategies to avoid undesirable reactions on the electrode surfaces. Our new electrode design can significantly reduce the formation of the surface reaction products, and thus greatly improve the cycling stability.  Excellent high rate capability and long cycle stability are obtained as compared with traditional electrodes. Specific examples will be provided for Li-S batteries, and the fundamental reaction mechanisms will be discussed.