The use of protic ionic liquids with cathodes for sodium-ion batteries

Herein, we report for the first time the use of a protic ionic liquid as a component of a new Na-ion battery electrolyte. The protic ionic liquid has been tested in combination with two different types of sodium-ion cathode materials, polyanionic Na3V2(PO4)3 and layered Na0.67Mn0.89Mg0.11O2, in order to reveal its impact on the electrode material electrochemical performance. The results evidence that this novel electrolyte performs very well in combination with a polyanionic electrode material, while it shows poor performance with a layered oxide material

Hard carbons for sodium-ion batteries: Structure, analysis, sustainability, and electrochemistry

Hard carbons are extensively studied for application as anode materials in sodium-ion batteries, but only recently a great interest has been focused toward the understanding of the sodium storage mechanism and the comprehension of the structure–function correlation. Although several interesting mechanisms have been proposed, a general mechanism explaining the observed electrochemical processes is still missing, which is essentially originating from the remaining uncertainty on the complex hard carbons structure. The achievement of an in-depth understanding of the processes occurring upon sodiation, however, is of great importance for a rational design of optimized anode materials. In this review, we aim at providing a comprehensive overview of the up-to-date known structural models of hard carbons and their correlation with the proposed models for the sodium-ion storage mechanisms. In this regard, a particular focus is set on the most powerful analytical tools to study the structure of hard carbons (upon de-/sodiation) and a critical discussion on how to interpret and perform such analysis. Targeting the eventual commercialization of hard carbon anodes for sodium-ion batteries – after having established a fundamental understanding – we close this review with a careful evaluation of potential strategies to ensure a high degree of sustainability, since this is undoubtedly a crucial parameter to take into account for the future large-scale production of hard carbons

Influence of electrochemical cycling on the rheo-impedance of anolytes for Li-based Semi Solid Flow Batteries

The recently launched concept of Semi-Solid Flow Batteries (SSFBs) shows a strong potential for flexible energy storage, but the liquid-dispersed state of the electrode materials introduces several aspects of which a scientific understanding is lacking. We studied the effect of electrochemical cycling on the rheological and electrical properties of a SSFB anolyte containing Li4Ti5O12 (LTO) and Ketjen Black (KB) particles in EC:DMC solvent with 1 M LiPF6, using an adapted rheometer that allows in situ electrochemical cycling and electrical impedance spectroscopy. Charging (lithiation) caused a reduction in the electronic conductivity, yield stress and high shear viscosity of the fluid electrode. For mildly reducing voltages (1.4 V), these changes were partially reversed on discharging. For more reducing voltages these changes were stronger and persistent. The finding of comparable trends for a fluid electrode without the LTO, lends support to a simplistic interpretation, in which all trends are ascribed to the formation of a surface layer around the conductive KB nanoparticles. This Solid Electrolyte Interphase (SEI) insulates particles and reduces the van der Waals attractions between them. SEI layers formed at less reducing voltages, partially dissolve during the subsequent discharge. Those formed at more reducing voltages, are thicker and permanent. As these layers increase the electronic resistance of the fluid electrode by (more than) an order of magnitude, our findings highlight significant challenges due to SEI formation that still need to be overcome to realize SSFBs

Intercalation Pseudocapacitance Boosting Ultrafast Sodium Storage in Prussian Blue Analogs

Great expectation is placed on sodium-ion batteries with high rate capability to satisfy multiple requirements in large-scale energy storage systems. However, the large ionic radius and high mass of Na + hamper its kinetics in the case of diffusion-controlled mechanisms in conventional electrodes. In this study, a unique intercalation pseudocapacitance has been demonstrated in low-vacancy copper hexacyanoferrate, achieving outstanding rate capability. The minimization of the [Fe(CN) 6 ] vacancy enables unhindered diffusion pathways for Na + and little structural change during the Fe 2+ /Fe 3+ redox reaction, eliminating solid-state diffusion limits. Moreover, the Cu + /Cu 2+ couple is unexpectedly activated, realizing a record capacity for copper hexacyanoferrate. A capacity of 86 mAh g −1 is obtained at 1 C, of which 50 % is maintained under 100 C and 70 % is achieved at 0 °C. Such intercalation pseudocapacitance might shed light on exploiting high-rate electrodes among Prussian blue analogs for advanced sodium-ion batteries