1:30pm - 2:00pmInvited
Hydrate-melt Electrolytes for High-voltage Aqueous Li-ion Batteries
1Department of Chemical System Engineering, The University of Tokyo, Japan; 2Elements Strategy Initiative for Catalysts and Batteries (ESICB), Kyoto University, Japan
Aqueous Li-ion batteries are attracting increasing attention as a safe energy-storage device using non-flammable aqueous electrolytes. However, their low voltage and low energy density, which result from the narrow potential window of water and the limited selection of suitable negative electrodes, are problematic for their future widespread application.
Here we discovered a room-temperature Li-salt hydrate melt, Li(TFSI)0.7(BETI)0.3∙2H2O, as a new class of aqueous liquid material that has a wide potential window over 3 V.1) The discovery of the Li-salt hydrate melt was achieved by the careful selection of suitable Li-salt anions (TFSI and BETI) and the exploration of the optimized eutectic system thereof (LiTFSI:LiBETI=7:3 by mol). The hydrate melt is a stable liquid phase, even though the water content is extremely low (dihydrate). Detailed spectroscopic and theoretical investigations revealed a unique liquid structure, in which all water molecules participate in Li+ hydration shells and their hydrogen-bonding network is fully destroyed. Hence, the hydrate melt no longer has the nature of bulk water that has beset all other aqueous electrolytes to limit their potential window.
Applying to aqueous Li-ion batteries, we found that the hydrate-melt electrolyte enables a reversible reaction at a low-potential and high-capacity Li4Ti5O12 negative electrode, which is currently used in commercial non-aqueous Li-ion batteries. As a result, we demonstrated, for the first time, the reversible charge-discharge cycling of 2.4 V-class (LiCoO2/Li4Ti5O12) and 3.1 V-class (LiNi0.5Mn1.5O4/Li4Ti5O12) aqueous Li-ion batteries, which are the highest voltage among all aqueous batteries exceeding that of a lead-acid battery. The discovery of the hydrate-melt electrolyte will open a new era of water-based mass energy storage, breaking away from flammable, expensive, and toxic organic solvents, which can potentially replace commercial non-aqueous Li-ion batteries with operating voltages of 2.4-3.7 V.
 Y. Yamada et al. and A. Yamada, Nature Energy, 1, 16129 (2016).
2:00pm - 2:30pmInvited
Novel Liquid and Soft Matter Electrolytes for Rechargeable Batteries
Indian Institute of Science, India
The efficiency of an electrochemical device depends greatly on the underlying redox processes occurring at both bulk and interfaces of various electroactive components. Redox processes are intrinsically correlated to the movement of charges viz. ions and electrons at varying length scales which eventually determine the effective electrochemical response of the device. Thus, critical understanding of charge transport is important and the outcomes should aid in the chemical design of advanced and multifunctional electroactive components. The materials design has major influences on charge transport and eventually affects the electrochemical function. This talk will focus on the importance of charge transport in electrolytes and how it can be tailored and optimized via chemical design of materials. The non-trivial charge transport in liquid and soft matter electrolytes, which also includes substantial influence of solvent dynamics, and their correlations with energy storage mechanism will be presented and discussed in the light of diverse electrolytic systems of relevance to monovalent (Li-ion, Li-S) and higher valent (Mg) rechargeable batteries.
2:30pm - 2:45pmOral
The Solvation Structure of Lithium Ions in an Ether Based Electrolyte Solution from First-Principles Molecular Dynamics
1Department of Physics, National University of Singapore, Singapore; 2Global Research Center for Environment and Energy Based on Nanomaterials Science, National Institute for Materials Science, Japan
Understanding the solvation and desolvation of Li ions at the miscrosopic level is of great importance, due their crucial role in the electrolytes of Li based secondary batteries. Particularly attractive candidates for an application in Li based secondary batteries, such as Li-ion, Li–S, and Li–O2 batteries, are Oligoether (glyme) based electrolytes. As the solvation structure of Li ions in a glyme based electrolyte has not been fully clarified yet, we are going to present a computational study on the solvation structure of lithium ions in the mixture of triglyme and lithium bis(trifluoromethylsulfonyl)-amide (LiTFSA) by means of molecular orbital and molecular dynamics calculations based on density functional theory. We found that, in the electrolyte solution composed of the equimolar mixture of triglyme and LiTFSA, lithium ions are solvated mainly by crown-ether-like curled triglyme molecules and in direct contact with an TFSA anion. We also found the aggregate formed with Li ion and TFSA anions and/or triglyme molecule(s) is equally stable, which has not been reported in the previous classical molecular dynamics simulations, suggesting that in reality a small fraction of Li ions form aggregates and they might have a significant impact on the Li ion transport. Our results demonstrate the importance of performing electronic structure based molecular dynamics of electrolyte solution to clarify the detailed solvation structure of the Li ion.
 M. Callsen, K. Sodeyama, Z. Futera, Y. Tateyama, I. Hamada, J. Phys. Chem. B 121, 180 (2017)
2:45pm - 3:00pmOral
Influence of Solid-Electrolyte Interfaces on Electronic and Ionic Dynamics in Porous Electrodes
1Institut de Recherche de Chimie Paris (IRCP), Centre Nationnal de la Recherche Scientifique (CNRS), Chimie ParisTech, France; 2Institut de Chimie Moléculaire et des Matériaux d'Orsay (ICMMO), Centre Nationnal de la Recherche Scientifique (CNRS), Université Paris Sud, France; 3GeePs, Centre Nationnal de la Recherche Scientifique (CNRS), CentraleSupelec, France; 4Institut des Matériaux Jean ROUXEL (IMN), Centre Nationnal de la Recherche Scientifique (CNRS), Université de Nantes, France
An understanding of the transport properties in composite porous electrodes is fundamental to improve the battery performance. The developments of new experimental techniques as well as methodologies are needed to understand the relationships between the composition, the architecture and the performance of composite electrodes. The fruitful contribution of Broadband Dielectric Spectroscopy (BDS) to study hierarchical materials applied to lithium ion and lithium metal batteries electrodes have been previously shown. The porous electrodes consist of a semiconductor active material (A), carbon (C) and a polymeric binder (B). The carbon (carbon black, fibers) is percolated in order to ensure a better electronic transfer in the material. The presence of a network of pores facilitates ion transfers when they are filled with a liquid electrolyte (E). Composite electrodes have architectures made up of agglomerates of C and A particles. However, the presence of interfaces AA, CC, AC, AE and CE modifies electronic transfer and ionic diffusion.
The simultaneous measurement of these charge transfers is carried out by in and ex situ (40 Hz to 10 GHz) dielectric spectroscopy which takes into account both the constraints imposed by the nature of the samples and the dynamics of the different charge carriers. Short- and long-range motions of ions are evidenced in the low-frequency region. At higher frequencies, the study shows for the first time the influence of the ions of the electrolyte on the transfer of the electronic charges (and conversely) at the micronic and nanometric scales. The new device opens thus important prospects to determine the evolutions of the multi-scales electrical properties during electrochemical cycling at different temperatures.
3:00pm - 3:15pmOral
Development of Prospective Electrode Materials for Na-ion and K-ion Batteries
1Deakin University, Australia; 2University of New South Wales, Australia
It is essential to develop new battery technologies based on natural elements with advantages of material abundance and eco-efficient synthetic processes. Along this line, sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs) have recently received renewed attention. Achieving a long-term stable cycle life with high reversible capacity and rate capability is one of the major challenges for electrode materials in both Na-ion and K-ion batteries. The larger sizes of Na+ (1.02 Å) and K+ (1.38 Å) than that of Li+ (0.76 Å) make them kinetically frustrated during their insertion and transport in the host lattices, which often results in poorer cycle life, lower capacity and rate capability and can be addressed by tuning the electrode host structure.
A simple, cheap and easily scalable synthesis approach is employed to create a unique hybrid cathode architecture of maricite NaFePO4/C/graphene which demonstrates outstanding sodium electrochemistry with a high reversible capacity of 142 mAh g-1 after long-term 300 cycles, corresponding to ~98 % capacity retention (very negligible capacity fading) of its initial cycle. A capacity retention of 79, 67, and 51 mAh g-1 can also be obtained with a high current rate of 1, 2, and 3C, respectively.
We have also developed a method to modify commercially available synthetic graphite. The modified graphite is used as anode in K-ion cells and demonstrates an outstanding long-term stability with a retained reversible capacity of 155 mAh g-1 at 100 mA g-1 after 700 cycles. Even more attractive de-potassiation (reversible) capacity of 197 mAh g-1 is achieved at a very high current of 4 A g-1 when potassiation is conducted at a fixed slow current rate.
In this presentation, we will talk about the importance of new electrodes and their synthesis method for the development of cost-effective and reliable storage options for renewable energy.
3:15pm - 3:30pmOral
Effect of Al2O3 Ceramic Filler on Thermal and Transport Properties of Poly(Ethylene Oxide)-Lithium Perchlorate Solid Polymer Electrolytes
1Department of Physics, University of Peradeniya, Sri Lanka; 2Postgraduate Institute of Science, University of Peradeniya, Sri Lanka; 3National Institute of Fundamental Studies, Sri Lanka
Polymer electrolytes (PEs) have attracted attention in the last two decades due to their applications in electrochemical devices. At low temperatures, the conductivity of PEs is poor due to the presence of crystalline PEO regions. Low molecular weight liquid plasticizers and ceramic fillers are added to overcome the above problems. In the present work poly(ethylene oxide) (PEO) was selected as host polymer and lithium perchlorate (LiClO4) was used as the salt and the effects of adding the inert filler alumina (Al2O3) to PEO-LiClO4 polymer electrolytes have been investigated. Ionic conductivity of PEs was measured using complex impedance spectroscopy. Maximum ionic conductivity was obtained for the n = 10 sample, (PEO)nLiClO4, out of the five samples (n = 10,20,30,40,60) studied. Al3O3 was added to the n = 10 and n =30 samples as a weight percentage (from 2.5% to 15%). An increase in ionic conductivity was obtained when the filler percentage was increased and further increase of filler content decreased the conductivity. This is connected with the increase of the amorphous phase content in the polymer with the addition of filler. Differential Scanning Calorimetry results indicate reduction of melting enthalpy and a slight shift in the melting temperature (Tm), towards lower values with the addition of salt concentration as well as with the addition of filler percentage, indicating the increase of amorphous nature of samples. An endothermic peak is observed at 69.7 °C, which corresponding to Tm of pure PEO. The complexation of LiClO4 salt with PEO was confirmed by Fourier Transform Infrared (FTIR) spectroscopy studies. It can be well observed that the increase in salt concentration and the addition of Al2O3 results in decrease of crystalline nature of the polymer electrolytes.