Influence of Porosity of Sulfide-Based Artificial Solid Electrolyte Interphases on Their Performance with Liquid and Solid Electrolytes in Li and Na Metal Batteries.

Realization of all-solid-state batteries combined with metallic Li/Na is still hindered due to the unstable interface between the alkali metal and solid electrolytes, especially for highly promising thiophosphate materials. Artificial and uniform solid-electrolyte interphases (SEIs), serving as thin ion-conducting films, have been considered as a strategy to overcome the issues of such reactive interfaces. Here, we synthesized sulfide-based artificial SEIs (LixSy and NaxSy) on Li and Na by solid/gas reaction between the alkali metal and S vapor. The synthesized films are carefully characterized with various chemical/electrochemical techniques. We show that these artificial SEIs are not beneficial from an application point of view since they either contribute to additional resistances (Li) or do not prevent reactions at the alkali metal/electrolyte interface (Na). We show that NaxSy is more porous than LixSy, supported by (i) its rough morphology observed by focused ion beam-scanning electron microscopy, (ii) the rapid decrease of Rinterface (interfacial resistance) in NaxSy-covered-Na symmetric cells with liquid electrolyte upon aging under open-circuit potential, and (iii) the increase of Rinterface in NaxSy-covered-Na solid-state symmetric cells with Na3PS4 electrolyte. The porous SEI allows the penetration of liquid electrolyte or alkali metal creep through its pores, resulting in a continuous chemical reaction. Hence, porosity of SEIs in general should be carefully taken into account in the application of batteries containing both liquid electrolyte and solid electrolyte.

Porosity of Solid Electrolyte Interphases on Alkali Metal Electrodes with Liquid Electrolytes.

Despite the fact that solid electrolyte interphases (SEIs) on alkali metals (Li and Na) are of great importance in the utilization of batteries with high energy density, growth mechanism of SEIs under an open-circuit potential important for the shelf life and the nature of ionic transport through SEIs are yet poorly understood. In this work, SEIs on Li/Na formed by bringing the electrodes in contact with ether- and carbonate-based electrolyte in symmetric cells were systematically investigated using diverse electrochemical/chemical characterization techniques. Electrochemical impedance spectroscopy (EIS) measurements linked with activation energy determination and cross-section images of Li/Na electrodes measured by ex situ FIB-SEM revealed the liquid/solid composite nature of SEIs, indicating their porosity. SEIs on Na electrodes are shown to be more porous compared to the ones on Li in both carbonate and glyme-based electrolytes. Nonpassivating nature of such SEIs is detrimental for the performance of alkali metal batteries. We laid special emphasis on evaluating time-dependent activation energy using EIS.

Roll-to-Roll Laser-Printed Graphene-Graphitic Carbon Electrodes for High-Performance Supercapacitors.

Carbon electrodes including graphene and thin graphite films have been utilized for various energy and sensor applications, where the patterning of electrodes is essentially included. Laser scribing in a DVD writer and inkjet printing were used to pattern the graphene-like materials, but the size and speed of fabrication has been limited for practical applications. In this work, we devise a simple strategy to use conventional laser-printer toner materials as precursors for graphitic carbon electrodes. The toner was laser-printed on metal foils, followed by thermal annealing in hydrogen environment, finally resulting in the patterned thin graphitic carbon or graphene electrodes for supercapacitors. The electrochemical cells made of the graphene-graphitic carbon electrodes show remarkably higher energy and power performance compared to conventional supercapacitors. Furthermore, considering the simplicity and scalability of roll-to-roll (R2R) electrode patterning processes, the proposed method would enable cheaper and larger-scale synthesis and patterning of graphene-graphitic carbon electrodes for various energy applications in the future.

Tin Sulfide-Based Nanohybrid for High-Performance Anode of Sodium-Ion Batteries.

Nanohybrid anode materials for Na-ion batteries (NIBs) based on conversion and/or alloying reactions can provide significantly improved energy and power characteristics, while suffering from low Coulombic efficiency and unfavorable voltage properties. An NIB paper-type nanohybrid anode (PNA) based on tin sulfide nanoparticles and acid-treated multiwalled carbon nanotubes is reported. In 1 m NaPF6 dissolved in diethylene glycol dimethyl ether as an electrolyte, the above PNA shows a high reversible capacity of ≈1200 mAh g-1 and a large voltage plateau corresponding to a capacity of ≈550 mAh g-1 in the low-voltage region of ≈0.1 V versus Na+ /Na, exhibiting high rate capabilities at a current rate of 1 A g-1 and good cycling performance over 250 cycles. In addition, the PNA exhibits a high first Coulombic efficiency of ≈90%, achieving values above 99% during subsequent cycles. Furthermore, the feasibility of PNA usage is demonstrated by full-cell tests with a reported cathode, which results in high specific energy and power values of ≈256 Wh kg-1 and 471 W kg-1 , respectively, with stable cycling.

A comparative study of graphite electrodes using the co-intercalation phenomenon for rechargeable Li, Na and K batteries.

Here, we demonstrate that graphite can serve as a versatile electrode for various rechargeable battery types by reversibly accommodating solvated alkali ions (such as K, Na, and Li) through co-intercalation in its galleries. The co-intercalation of alkali ions is observed to occur via staging reactions. Notably, their insertion behaviors, including their specific capacity, are remarkably similar regardless of the alkali ion species despite the different solubility limits of K, Na, and Li ions in graphite. Nevertheless, the insertion potentials of the solvated alkali ions differ from each other and are observed to be correlated with the interlayer distance in the intercalated graphite gallery.