Challenges and Strategies for High-Energy Aqueous Electrolyte Rechargeable Batteries.

Aqueous rechargeable batteries are becoming increasingly important to the development of renewable energy sources, because they promise to meet cost-efficiency, energy and power demands for stationary applications. Over the past decade, efforts have been devoted to the improvement of electrode materials and their use in combination with highly concentrated aqueous electrolytes. Here the latest ground-breaking advances in using such electrolytes to construct aqueous battery systems efficiently storing electrical energy, i.e., offering improved energy density, cyclability and safety, are highlighted. This Review aims to timely provide a summary of the strategies proposed so far to overcome the still existing hurdles limiting the present aqueous batteries technologies employing concentrated electrolytes. Emphasis is placed on aqueous batteries for lithium and post-lithium chemistries, with potentially improved energy density, resulting from the unique advantages of concentrated electrolytes.

Electrochemical Reactivity and Passivation of Silicon Thin-Film Electrodes in Organic Carbonate Electrolytes.

This work focuses on the mechanisms of interfacial processes at the surface of amorphous silicon thin-film electrodes in organic carbonate electrolytes to unveil the origins of the inherent nonpassivating behavior of silicon anodes in Li-ion batteries. Attenuated total reflection Fourier-transform infrared spectroscopy, X-ray absorption spectroscopy, and infrared near-field scanning optical microscopy were used to investigate the formation, evolution, and chemical composition of the surface layer formed on Si upon cycling. We found that the chemical composition and thickness of the solid/electrolyte interphase (SEI) layer continuously change during the charging/discharging cycles. This SEI layer "breathing" effect is directly related to the formation of lithium ethylene dicarbonate (LiEDC) and LiPF6 salt decomposition products during silicon lithiation and their subsequent disappearance upon delithiation. The detected appearance and disappearance of LiEDC and LiPF6 decomposition compounds in the SEI layer are directly linked with the observed interfacial instability and poor passivating behavior of the silicon anode.

Understanding the Electrode/Electrolyte Interface Layer on the Li-Rich Nickel Manganese Cobalt Layered Oxide Cathode by XPS.

Layered lithium-rich nickel manganese cobalt oxide (LR-NMC) represents one of the most promising cathode materials for application in high energy density lithium-ion batteries. The extraordinary capacity delivered derives from a combination of both cationic and anionic redox processes. However, the latter ones lead to oxygen evolution which triggers structural degradation and electrode/electrolyte interface (EEI) instability that hinders the use of LR-NMC in practical application. In this work, we investigate the surface chemistry of LR-NMC and its evolution upon different conditions to give further insights into the processes occurring at the EEI. X-ray photoelectron spectroscopy studies reveal that once the organic component of the layer is formed, it remains stable independently on the higher cutoff voltage applied, while continuous growth of inorganics along with oxygen evolution occurs. The results performed on lithiated and delithiated LR-NMC surfaces indicate an instability of the EEI layer formed at high voltages, which undergoes a partial decomposition. Furthermore, the tris(pentafluorophenyl)borane electrolyte additive simultaneously prevents excess LiF formation and changes the chemical composition of the EEI layer. The latter is characterized by a higher amount of poly(ethylene oxide) oligomer species and LixPOyFz formation. In addition, the presence of boron-containing compounds in the EEI layer cannot be excluded, which may be also responsible of the increased thickness of the EEI layer. Finally, fast kinetics at elevated temperatures exacerbate the salt decomposition which results in the formation of an EEI which is thicker and richer in LiF.

Ionic Liquid-Based Electrolytes for Sodium-Ion Batteries: Tuning Properties To Enhance the Electrochemical Performance of Manganese-Based Layered Oxide Cathode.

Ionic liquids (ILs) are considered as appealing alternative electrolytes for application in rechargeable batteries, including next-generation sodium-ion batteries, because of their safe and eco-friendly nature, resulting from their extremely low volatility. In this work, two groups of advanced pyrrolidinium-based IL electrolytes are concerned, made by mixing sodium bis(fluorosulfonyl)imide (NaFSI) or sodium bis(trifluoromethanesulfonyl)imide (NaTFSI) salts salts with N-methyl- N-propylpyrrolidinium bis(fluorosulfonyl)imide (Pyr13FSI), N-butyl- N-methylpyrrolidinium bis(fluorosulfonyl)imide (Pyr14FSI), and N-butyl- N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (Pyr13FSI). The characterization of eight different electrolytes, including single anion electrolytes and binary anion mixtures, in terms of thermal properties, density, viscosity, and conductivity, as well as electrochemical stability window and cycling performance in room-temperature sodium cells, is reported here. Among all of the blends, those containing Pyr14FSI outperform the others in terms of cell performance enabling the layered P2-Na0.6Ni0.22Al0.11Mn0.66O2 cathode to deliver about 140 mAh g-1 for more than 200 cycles.

Impact of the Acid Treatment on Lignocellulosic Biomass Hard Carbon for Sodium-Ion Battery Anodes.

The investigation of phosphoric acid treatment on the performance of hard carbon from a typical lignocellulosic biomass waste (peanut shell) is herein reported. A strong correlation is discovered between the treatment time and the structural properties and electrochemical performance in sodium-ion batteries. Indeed, a prolonged acid treatment enables the use of lower temperatures, that is, lower energy consumption, for the carbonization step as well as improved high-rate performance (122 mAh g-1 at 10 C).

Pectin, Hemicellulose, or Lignin? Impact of the Biowaste Source on the Performance of Hard Carbons for Sodium-Ion Batteries.

Hard carbons are currently the most widely used negative electrode materials in Na-ion batteries. This is due to their promising electrochemical performance with capacities of 200-300 mAh g-1 and stable long-term cycling. However, an abundant and cheap carbon source is necessary in order to comply with the low-cost philosophy of Na-ion technology. Many biological or waste materials have been used to synthesize hard carbons but the impact of the precursors on the final properties of the anode material is not fully understood. In this study the impact of the biomass source on the structural and electrochemical properties of hard carbons is unraveled by using different, representative types of biomass as examples. The systematic structural and electrochemical investigation of hard carbons derived from different sources-namely corncobs, peanut shells, and waste apples, which are representative of hemicellulose-, lignin- and pectin-rich biomass, respectively-enables understanding and interlinking of the structural and electrochemical properties.

A comparative study of layered transition metal oxide cathodes for application in sodium-ion battery.

Herein, we report a study on P-type layered sodium transition metal-based oxides with a general formula of NaxMO2 (M = Ni, Fe, Mn). We synthesize the materials via coprecipitation followed by annealing in air and rinsing with water, and we examine the electrodes as cathodes for sodium-ion batteries using a propylene carbonate-based electrolyte. We fully investigate the effect of the Ni-to-Fe ratio, annealing temperature, and sodium content on the electrochemical performances of the electrodes. The impact of these parameters on the structural and electrochemical properties of the materials is revealed by X-ray diffraction, scanning electron microscopy, and cyclic voltammetry, respectively. The suitability of this class of P-type materials for sodium battery application is finally demonstrated by cycling tests revealing an excellent electrochemical performance in terms of delivered capacity (i.e., about 200 mAh g(-1)) and charge-discharge efficiency (approaching 100%).

Sodium-ion battery based on an electrochemically converted NaFePO4 cathode and nanostructured tin-carbon anode.

We report a new sodium-ion battery formed by coupling a NaFePO(4) cathode and a nanocomposite tin-carbon (Sn-C) sodium-alloying anode. The NaFePO(4) cathode is obtained by Li-Na conversion of a LiFePO(4) cathode directly in the full cell employing the Sn-C anode and a sodium-ion electrolyte. The results show that the unique approach adopted here is capable of successfully and efficiently converting LiFePO(4) into NaFePO(4) in a sodium-ion battery operating at a voltage of 3 V, with a maximum reversible capacity of 150 mAh g(-1), high reversibility, and high rate capability.