Ionic Liquid-Based Electrolyte Membranes for Medium-High Temperature Lithium Polymer Batteries

Li+-conducting polyethylene oxide-based membranes incorporating N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide are used as electrolyte separators for all-solid-state lithium polymer batteries operating at medium-high temperatures. The incorporation of the ionic liquid remarkably improves the thermal, ion-transport and interfacial properties of the polymer electrolyte, which, in combination with the wide electrochemical stability even at medium-high temperatures, allows high current rates without any appreciable lithium anode degradation. Battery tests carried out at 80 °C have shown excellent cycling performance and capacity retention, even at high rates, which are never tackled by ionic liquid-free polymer electrolytes. No dendrite growth onto the lithium metal anode was observed

Sodium Biphenyl as Anolyte for Sodium-Seawater Batteries

Sodium-based battery systems have recently attracted increasing research interest due to the abundant resources employed. Among various material candidates for the negative electrode, sodium metal provides the highest capacity of theoretically 1165 mAh g(-1) and a very low redox potential of -2.71 versus the standard hydrogen electrode. However, the high reactivity of sodium metal toward the commonly used electrolytes results in severe side reactions, including the evolution of gaseous decomposition products, and, in addition, the risk of dendritic sodium growth, potentially causing a disastrous short circuit of the cell. Herein, the use of sodium biphenyl (Na-BP) as anolyte for the Na-seawater batteries (Na-SWB) is investigated. The catholyte for the open-structured positive electrode is natural seawater with sodium cations dissolved therein. Remarkably, the significant electronic and ionic conductivities of the Na-BP anolyte enable a low overpotential for the sodium deposition upon charge, allowing for high capacity and excellent capacity retention for 80 cycles in full Na-SWB. Additionally, the Na-BP anolyte suppresses gas evolution and dendrite growth by forming a homogeneous surface layer on the metallic negative electrode

A beneficial combination of formic acid as a processing additive and fluoroethylene carbonate as an electrolyte additive for Li4_{4}Ti5_{5}O12_{12} lithium-ion anodes

The aqueous processing of lithium transition metal oxide active materials such as Li$_{4}$Ti$_{5}$O$_{12}$ (LTO) into electrodes remains a challenge owing to the high reactivity of such materials in contact with water, resulting in a rapid pH increase, aluminum current collector corrosion, and inferior cycling stability. Herein, the addition of formic acid (FA) as an electrode slurry processing additive is investigated, including a variation of the mixing speed as an additional important parameter. Following the identification of suitable electrode preparation conditions, the effect of fluoroethylene carbonate (FEC) as an electrolyte additive is studied in half-cells and full-cells comprising a LiNi$_{0.5}$Mn$_{0.3}$Co$_{0.2}$O$_{2}$ (NMC$_{532}$) based positive electrode. Owing to the beneficial impact of FEC on the solid electrolyte interphase (SEI) formed at the LTO|electrolyte interface, involving specifically the suppression of lithium salt decomposition, both the half-cells and the LTO‖NMC$_{532}$ full-cells exhibit a superior performance, achieving a capacity retention of 84.3% and 64.1% after 5000 and 10 000 cycles at 2C, respectively

Anode-less seawater batteries with a Na-ion conducting solid-polymer electrolyte for power to metal and metal to power energy storage

Seawater batteries (SWBs) have been mostly researched for large scale energy storage and (sub-)marine applications. In a SWB, the aqueous catholyte (seawater) and a non-aqueous anolyte (aprotic solvent solution) are physically separated by a NASICON solid electrolyte membrane. Given the practically unlimited Na+ ion supply from seawater, the energy storage is only limited by the amount of Na stored in the negative electrode. Therefore, the highest volumetric and gravimetric energy densities can be achieved by storing Na metal without the need for a host material. To achieve safe realization of such a cell, a compact, metal-less anode design is herein demonstrated for the first time. The anode compartment integrates the NASICON solid electrolyte, a Na-ion conductive solid-state polymer electrolyte (Na-SPE), having a high ionic conductivity (over 1 mS cm−1 at moderate room temperature), and a negative electrode current collector. The reactive Na metal is not employed in the cell construction, but it is harvested from seawater upon charge (power to metal) and reconverted into energy upon the discharge process (metal to power). The overall round-trip energy efficiency (RTE) of the devices is over 85% at room temperature

Study of water-based lithium titanate electrode processing: the role of pH and binder molecular structure

This work elucidates the manufacturing of lithium titanate (Li$_{4}$Ti$_{5}$O$_{12}$, LTO) electrodes via the aqueous process using sodium carboxymethylcellulose (CMC), guar gum (GG) or pectin as binders. To avoid aluminum current collector dissolution due to the rising slurries’ pH, phosphoric acid (PA) is used as a pH-modifier. The electrodes are characterized in terms of morphology, adhesion strength and electrochemical performance. In the absence of phosphoric acid, hydrogen evolution occurs upon coating the slurry onto the aluminum substrate, resulting in the formation of cavities in the coated electrode, as well as poor cohesion on the current collector itself. Consequently, the electrochemical performance of the coated electrodes is also improved by the addition of PA in the slurries. At a 5C rate, CMC/PA-based electrodes delivered 144 mAh·g$^{-1}$, while PA-free electrodes reached only 124 mAh·g$^{-1}$. When GG and pectin are used as binders, the adhesion of the coated layers to the current collector is reduced; however, the electrodes show comparable, if not slightly better, electrochemical performance than those based on CMC. Full lithium-ion cells, utilizing CMC/PA-made Li[Ni$_{0.33}$Mn$_{0.33}$Co$_{0.33}$]O$_{2}$ (NMC) cathodes and LTO anodes offer a stable discharge capacity of ~120 mAh·g$^{ 1}$$_{(NMC)}$ with high coulombic efficiencies

Redox-Mediated Red-Phosphorous Semi-Liquid Anode Enabling Metal-Free Rechargeable Na-Seawater Batteries with High Energy Density

Sodium-seawater batteries (Na-SWB) are considered among the most promising electrochemical devices for large-scale energy storage and the marine sector. In fact, by employing an open-structured cathode, they benefit from the unlimited supply of sodium from seawater. This means, that the energy of such systems is intrinsically limited by the capacity of the anode. In order to increase the energy of Na-SWB, it is therefore necessary to introduce a high-capacity anode such as, e.g., red phosphorus. However, due to its large volume changes upon charge/discharge processes, obtaining thick electrodes and large areal capacity is extremely challenging. Herein, the areal/absolute capacity of the red phosphorus anode is increased by employing a semi-liquid electrode, which includes two redox mediators, i.e., sodium-biphenyl and sodium-pyrene, as reducing and oxidizing species for the exploitation of the full red phosphorus capacity. As a result, the red phosphorus semi-liquid anode in Na-SWB provides a high-capacity of 15 mAh cm(-2) in a static anode, showing great energy storage potential for operation in flow-mode when storing the semi-liquid negative electrode in a storage tank

Adaptive Multi‐Site Gradient Adsorption of Siloxane‐Based Protective Layers Enable High Performance Lithium‐Metal Batteries

Low Coulombic efficiency and significant capacity decay resulting from an unstable solid electrolyte interphase (SEI) and dendritic growth pose challenges to the practical application of lithium-metal batteries. In this study, a highly efficient protection layer induced by octaphenylsilsesquioxane (OPS) with LiFSI salt is investigated