Li-sulfur Batteries Research Articles

The Effect of Interactions and Reduction Products of LiNO3, the Anti-Shuttle Agent, in Li-S Battery Systems

Sulfur cathodes have excellent theoretical properties for use as positive electrodes in rechargeable lithium batteries. However they suffer from an internal redox shuttle process which limit their capacity because the sulfur reduction products, LixSy species, cannot be fully re-oxidized. In order to overcome this problem, lithium nitrate is commonly used as an additive to the electrolyte solution, suppressing the shuttle phenomena in Li-sulfur batteries. We rigorously studied the electrochemical behavior of LiNO3 in electrolyte solutions and with electrodes relevant to Li-S cells. EQCM UV-Vis and XPS spectroscopies were used in conjunction with standard electrochemical measurements, in order to determine the stability limits of this additive. An irreversible reduction of the nitrate species occurs in Li-S cells resulting in a precipitation of electrolyte solutions decomposition products such as LiF and oxygen-containing polymeric species formed by reactions of the ethereal solutions due to nitrate reduction on the cathode side below 1.9 V vs. Li .We showed that both the reversible capacity and the voltage profile of Li-S cells are significantly improved when the limiting cutoff potentials for the sulfur cathodes is set above the red-ox potential of LiNO3.

The effect of V2O5/C additive on the suppression of polysulfide dissolution in Li-sulfur batteries

The effect of adding a V2O5/carbon nano-composite to the cathode of a Li-sulfur battery on suppressing the polysulfide dissolution phenomenon was evaluated by comparing the amount of overcharge at the first discharge–charge processes. V2O5/carbon nano-composite was manufactured by forming V2O5 ⋅H2O xerogel on the carbon black through a simple wet process. This provides a high surface area with plenty of hydrophilic moieties that can capture and store soluble polysulfides on its surface during the discharge–charge reactions, and also partly contributes to suppressing the excessive formation of Li2S which undergoes a large volume change during the cycling. From the electrochemical results, we could observe a significant reduction in the overcharge amount and improved cyclic performance by adding as little as 2 % of the nano-composite. UV–VIS spectra measured after a small addition of the nano-composite to the solution containing Li2S6 polysulfide also confirmed that the V2O5/carbon nano-composite is highly effective in capturing long-chain polysulfides on its surface.

Applications of Dendrimer-Based Nano-Architectures in Li-Air and Li-Sulfur Batteries

Dendritic branched polymers, particularly the well studied, most commonly synthesized and commercially available polyamidoamine (PAMAM) dendrimers have a high degree of surface functionalities, high surface-area, large molecular weights, and ample well-defined interior space. Additionally, due to their high porosities, high room temperature ionic conductivities of their lithium (Li) salts, and good chemical and thermal stabilities, they may provide improved properties as potential electrode materials and polymer electrolytes. PAMAM dendrimers are particularly attractive candidates as templates for the synthesis of catalyst metal nanoparticles due to a high density of interior tertiary amines, which are able to complex with metal ions and variable surface groups to tailor their solubility. These remarkable physico-chemical properties of dendrimers enable them to be applied in next-generation energy storage technologies.Amongst all sustainable rechargeable Li-batteries, Li-air (Li-O2) and Li-sulfur (Li-S) batteries are the most promising with very high specific energy densities (11,140 Wh/kg and 2,600 Wh/kg respectively). However, several fundamental issues hinder their commercialization. Oxidation of the insoluble, poorly conducting Li2O2 discharge products during charging, slow kinetics of the oxygen reduction reaction during discharge, and the oxygen evolution reaction (OER) during charging resulting in low round-trip efficiency of the battery, high voltage required during the OER process leading to degradation of non-aqueous electrolytes and carbon-based air electrodes resulting in rapid capacity fade and further increasing the discharge-charge voltage hysteresis in the battery are some of the critical challenges with the Li-O2 battery. In Li-S batteries, the charge/discharge reaction creates highly soluble polysulfide intermediates in electrolytes, causing irreversible loss of active sulfur and low cycling efficiency. Furthermore, the battery’s cycle life and safety can be greatly improved by replacing liquid electrolytes with gel or solid polymer electrolytes.Here, we will discuss a fundamental understanding of branched polymers as advanced energy storage materials expanding their applications to sustainable high-energy density storage and conversion systems such as those mentioned above. Specifically, dendrimer-encapsulated ruthenium nanoparticles (DEN-Ru) were used as catalysts in Li-O2 batteries for the first time. The DEN-Ru significantly improves the cycling stability of Li-O2 batteries with carbon black electrodes and decreases the charging potential even at low catalyst loading. Furthermore, the potential of using DEN-Ru as a standalone cathode material for Li-O2 batteries also will be discussed.Additionally, we also explored the application of chemically modified PAMAM dendrimers with electronic conductivity in Li-S batteries. These modified dendrimers showed a better cycling stability compared with hyperbranched polymers used as cathode materials.We will also discuss the potential of ionically conducting dendrimers as electrolyte systems. Detailed characterizations of these novel nano-architectures will be discussed to understand how their structure and chemistry influence the electrochemical performance of the aforementioned energy systems. It is anticipated that by using novel dendrimer chemistry and assembly, our research will lead to the development of energy materials that embody the nanoscale properties of soft and porous dendritic nanostructures and provide innovative solutions for improving the state‐of‐the‐art of sustainable, high energy density applications.

Tailoring interactions of carbon and sulfur in Li–S battery cathodes: significant effects of carbon–heteroatom bonds

In this study, effects of carbon–heteroatom bonds on sulfur cathodes were investigated. A series of carbon black substrates were prepared using various treatments to introduce nitrogen or oxygen surface species. Our results indicated that nitrogen-doped carbon black significantly improved the electrochemical performance of sulfur cathode materials. Synchrotron-based XPS revealed that the defect sites of nitrogen-doped carbon are favorable for the discharge product deposition, leading to a high utilization and reversibility of sulfur cathodes. Our studies also found that the introduction of oxygen functional groups results in deteriorated performance of Li–sulfur batteries due to the reduced conductivity and unwanted side reactions occurring between sulfur and surface oxygen species.

Li-S Cathodes with Extended Cycle Life By Sulfur Encapsulation in Disordered Micro-Porous Carbon Powders

Sulfur cathodes have excellent theoretical properties for use as positive electrodes in rechargeable lithium batteries, but lack long-term stability required of practical secondary battery systems. To deal with this issue, high capacity Lithium-Sulfur cathodes with extended cycle life were prepared through thermal encapsulation of sulfurat 155°C in disordered micro-porous carbon powders that have high specific surface-area of ~ 2000 m2/g. The electrodes have been characterized using X-ray diffraction (XRD), Scanning electron microscopy/energy-dispersive X-ray (SEM/EDX), Raman spectroscopy, Thermal Gravimetric Analysis (TGA) and Gas adsorption technique. By using microporous carbon as matrices for sulfur cathodes and lithium nitrate as an additive to the electrolyte solution, that suppresses the shuttle phenomena in Li-sulfur batteries, we managed to achieve a reversible capacity of over 500mAh/g after 1000 cycles (Figure 1) with a Columbic efficiency approaching 100% throughout cycling. The sulfur composite cathodes of 14mm in diameter (area of ~1.54 cm2) and active material load of more than 1mg/cm2were tested in a two electrodes configuration with coin-type cells (2523,NRC, Canada). Electrolyte solution was DOL and DME (1:1 ratio) with 10% LiTFSI and 2% of LiNO3(by weight).The influence of the volume of the electrolyte solutions in Li-S cells was further evaluated by analyzing their voltage profiles during cycling.

Investigation of Lithium Solvated Ionic Liquid for High Performance Li-S Batteries

1:1 equimolar complex electrolytes composed of low-molecular-weight ether (glyme) and Li salt have been reported to exhibit high thermal and electrochemical stability due to strong interactions between the oxygen in the ether and the Li cation (Li salt glyme solvate ionic liquids) [1]. Favorable performances were achieved using 3V-class [LiFePO4 | Li metal] and 4V-class [LiNi1/3Mn1/3Co1/3O2 | Li metal] cells [2]. Moreover, Li salt glyme solvate ionic liquids have a weak coordinating ability, which allows for innovative Li-sulfur batteries with a long cycle life (over 400 cycles) by suppressing the dissolution of polysulfide and redox shuttle [3]. More specifically, it is becoming clear that Li salt glyme solvate ionic liquids have important performance benefits besides their safety. In previous research, we used electrochemical quartz crystal microbalance (EQCM) measurements to show that an observed decrease in local viscosity near the electrode-electrolyte interface is attributable to the concentration distribution of Li salt and the transitional liberation of glyme molecules during the deposition of Li metal [4]. Therefore, to improve the electrochemical stability and polysulfide solubility of Li salt glyme solvate ionic liquids, it is necessary to form long-lived robust complexes between oxygen in the ether electrolyte and Li cations. So, we propose Li salt glyme solvate ionic liquids that are non-equimolar and that are prepared by adding Li salts to achieve a higher Li salt concentration than that in the original 1:1 equimolar complex of glyme and Li salt. Moreover, we investigated relationships between sulfur positive electrode (composite material of elemental sulfur and high surface area carbon) and Li-S battery performances. In the presentation, we will report the relationships between Li-S battery performances and electrolyte / electrode materials.This study was supported by ALCA project, from JST, Japan.[1] K. Yoshida, M. Nakamura, Y. Kazue, N. Tachikawa, S. Tsuzuki, S. Seki, K. Dokko, M. Watanabe, J. Am. Chem. Soc., 133, 13121 (2001).[2] S. Seki, N. Serizawa, K. Takei, K. Dokko, M. Watanabe, J. Power Sources, 243, 323 (2013).[3] K. Dokko, N. Tachikawa, K. Yamauchi, M. Tsuchiya, A. Yamazaki, E. Takashima, J-W. Park, K. Ueno, S. Seki, N. Serizawa, M. Watanabe, J. Electrochem. Soc., 160, A1304 (2013).[4] N. Serizawa, S. Seki, K. Takei, H. Miyashiro, K. Yoshida, K. Ueno, N. Tachikawa, K. Dokko, Y. Katayama, M. Watanabe, T. Miura, J. Electrochem. Soc., 160, A1529 (2013).

Li Ion-Sulfur Batteries with Glyme-Lithium Salt Solvate Ionic Liquid Electrolytes

We have reported that equimolar mixtures of certain Li salts and glymes (triglyme (G3) and tetraglyme (G4)) form molten complexes at ambient temperature, and behave like typical ionic liquids (ILs).1,2 In the mixtures, ligand glyme molecules strongly coordinate (or solvate) to Li+ ions to form complex cations, hence, this family is classified as “solvate” ILs. Because complexation of appropriate Li salts with appropriate glymes allows realizing ILs involving Li+ ions as single cationic species, lithium solvate ILs possess high Li+ ion conductivity and transference number. In addition, the dissolution of lithium polysulfides (Li2S m ), the discharge products of elemental sulfur, was suppressed in certain solvate ILs due to their extremely low coordinating nature. Owing to these remarkable properties, they are fascinating electrolytes for Li-sulfur batteries.3,4 Recently, we found that solvate IL electrolyte allows successful charge-discharge of graphite electrode. These results inspire us to develop low-cost and safe batteries without Li metal anode. In this study, the battery performance of the graphite-sulfur full cells with the solvate IL electrolytes was evaluated employing a lithiated graphite (LiC6) anode or a lithiated sulfur (lithium sulfide, Li2S) cathode as a lithium source. A LiC6 anode and a Li2S cathode were prepared by chemical and electrochemical methods. Using these electrodes, two kinds of full cells in both charge and discharge states were fabricated. Reversible charge-discharge of both full cells can be performed at 60 ºC, however, the capacities decrease as repeating cycles and the coulombic efficiency for these cells is substantially low compared to our previous results. This is because relatively high operation temperature facilitate dissolution of elemental sulfur and/or Li2S m , leading to loss of active materials and undesired side-reactions. To overcome these problems, solvate IL electrolytes were diluted by an appropriate solvent with low donor ability. As a result, a stable cycle operation with a discharge capacity of 700–800 mA h g−1 and a coulombic efficiency of 90–95 % at 30 ºC was achieved over 100 cycles (Figure 1), irrespective of starting charge-discharge states.

Invited Presentation: Lithium Metal Anode: Challenges and Opportunities

Research on lithium metal combined with polymer electrolyte in lithium rechargeable batteries was started in 1979. Since that time, battery research has expanded worldwide. Several new polymers, solid electrolytes and ionic liquids with improved conductivity were identified. These advances resulted from a better understanding of the major parameters controlling ion migration, such as favorable polymer structure, phase diagram between solvating polymer and lithium salt, and the development of new lithium counter-anions. In spite of the progress so far, the quest for a highly conductive dry polymer at room temperature is still not available. However, effort is continuing, and all-lithium polymer battery (LPB) developers presently face the challenge of whether to heat the polymer electrolyte to enable high-power performance, as required for electric vehicle and energy storage. LPB developers have explored both the high-temperature and low-temperature options.This presentation discusses the challenges and opportunities in developing thin lithium metal with stable SEI as negative electrode for three battery technologies using:1. Batteries made from dry polymer and ionic liquid-polymer electrolytes forrechargeable lithium batteries2. All solid-state Li-sulfur batteries 3. Li-air batteries.In addition, we will discuss the safety of lithium, dendrite mechanism, interface phenomena, side reactions, protection of lithium metal, and lithium alloys.

Invited Presentation: Ionic Liquid Based Electrolytes for Li-Sulfur Batteries

Li-Sulfur (LiS) technology has great potential for large-scale energy storage applications due to the very high theoretical capacity. However, the implementation of the concept has been limited due to low sulphur utilization, severely decreasing the practical energy density, and poor cyclability in terms of fading capacity and rate capability. One major cause of these problems is the relatively large solubility of polysulfides (Li2Sn, n≥3) in the commonly used electrolyte systems. A direct consequence is the loss of active cathode material decreasing the capacity and at the same time increasing the resistance of the electrolyte. The dissolved polysulphides also cause degradation of the anode through shuttle reactions when they migrate in the electrolyte, forming insoluble layers on the anode surface.The materials problems in the LiS battery can be addressed by new concepts for both the electrolyte and the cathode. For development of the electrolyte promising approaches include moving away from traditional organic solvents, improving both performance and safety. In addition the use of polymer gel-polymer, or solid-polymer, electrolytes or ceramic electrolytes has also been proposed to prevent, in particular, the shuttle reactions.Ionic liquids have been highlighted as base for new and safe electrolytes [1]. Ionic liquids are low melting salts with intrinsic properties such as high ionic conductivity, low vapour pressure, and high thermal, chemical and electrochemical stability. Thus, they have the potential to both improve the performance and the safety of Li-ion and LiS-batteries. Ionic liquids can be used both to fully replace organic solvents as electrolyte solution or as co-solvents/additives improving both safety and performance. An ionic liquid-based electrolyte solution can also readily be incorporated in gel-type polymer membranes [2].In this contribution we present new results on the use of ionic liquids as base for electrolytes in LiS-batteries. We have investigated systems based purely on ionic liquids, mixed electrolytes, where ionic liquids partially replace an organic solvent, and the recently proposed “solvated ionic liquids” [3]. In particular we focus on the dissolution and speciation of polysulfides in the electrolyte solution. One key issue is the role of polysulfides present in the electrolyte for the formation and stability of surface films on Li-anodes [4]. We also report results of the compatibility of the electrolytes with new nanostructured and functionalized sulphur carbon composite electrodes.[1] A. Matic and B. Scrosati, MRS Bulletin38, 533 (2013)[2] J. Pitawala, M. Assunta Navarra, B. Scrosati, P. Jacobsson and A. MaticJournal of Power Sources, 245, 830-835 (2013)[3] K. Ueno, K. Yoshida, M. Tsuchiya, N. Tachikawa, K. Dokko, and M. Watanabe, J. Phys. Chem. B 116, 11323 (2012)[4] S. Xiong, K. Xie, E. Blomberg, P. Jacobsson, and Aleksandar MaticJournal of Power Sources, 252, 150 (2014)

Li-S Cathodes with Extended Cycle Life by Sulfur Encapsulation in Disordered Micro-Porous Carbon Powders

Sulfur cathodes have excellent theoretical properties for use as positive electrodes in rechargeable lithium batteries, but lack long-term stability required of practical secondary battery systems. To deal with this issue, high capacity Lithium-Sulfur cathodes were prepared through sulfur impregnation of disordered micro-porous carbon powders that have high surface-area. By using microporous carbon as a matrix for sulfur cathodes and lithium nitrate as an additive to the electrolyte solution, that suppresses the shuttle phenomena in Li-sulfur batteries, we managed to achieve a reversible capacity of over 500 mAh/g for 1000 cycles with a Columbic efficiency approaching 100% throughout cycling. The influence of the volume of the electrolyte solutions in Li-S cells was further evaluated by analyzing their voltage profiles during cycling.

Nanoscale stabilization of Li–sulfur batteries by atomic layer deposited Al2O3

An atomic layer deposited (ALD) Al2O3 coating applied to sulfur cathodes has been studied in this paper. It is demonstrated that the Al2O3 coating improves the cycling stability of Li–sulfur batteries. The underlying mechanism by synchrotron-based X-ray photoelectron spectroscopy was investigated. The coating layer not only protects the polysulfide from dissolution, but also facilitates the utilization of sulfur, demonstrating improved electrochemical performances.

All-solid-state Li–sulfur batteries with mesoporous electrode and thio-LISICON solid electrolyte

All-solid-state lithium–sulfur batteries were developed using elemental sulfur as a positive electrode, Li–Al alloy as a negative electrode, thio-LISICON as a solid electrolyte, and mesoporous carbon (CMK-3) as the framework for the positive electrode. The mesoporous framework provided high electrical conduction and improved electrode utilization. The sulfur provided a high reversible capacity and high current charge discharge characteristics. Sulfur introduced into the pore structure of the mesoporous carbon interacts with edges of the graphene sheet and both the sulfur and graphene layers participate in a highly reversible reaction.

Structure-Related Electrochemistry of Sulfur-Poly(acrylonitrile) Composite Cathode Materials for Rechargeable Lithium Batteries

The structure of sulfur-poly(acrylonitrile)-based Li-sulfur batteries is elucidated and correlated with the electrochemical performance of such devices. Apart from the poly(acrylonitrile)-derived backbone, thioamide as well as poly(sulfide) structures are proposed. Furthermore, the intermediary formation of S8 during cycling and the role of the electrolyte in its reintegration during charging into are addressed. In summary, a comprehensive picture of the chemistry and electrochemistry of Li-sulfur batteries is presented.

Lithium-air and lithium-sulfur batteries

Abstract

Protected Metallic Lithium Anodes for Li-Air and Li-Sulfur Batteries

not Available.

On the Surface Chemical Aspects of Very High Energy Density, Rechargeable Li-Sulfur Batteries

not Available.

On the Surface Chemical Aspects of Very High Energy Density, Rechargeable Li–Sulfur Batteries

Li(metal)–sulfur (Li–S) systems are among the rechargeable batteries of the highest possible energy density due to the high capacity of both electrodes. The surface chemistry developed on Li electrodes in electrolyte solutions for Li–S batteries was rigorously studied using Fourier transform infrared and X-ray photoelectron spectroscopies. A special methodology was developed for handling the highly reactive Li samples. It was possible to analyze the contribution of solvents such as 1-3 dioxolane, the electrolyte , polysulfide , and additives to protective surface films that are formed on the Li electrodes. The role of as a critical component whose presence in solutions prevents a shuttle mechanism that limits the capacity of the sulfur electrodes is discussed and explained herein.