Layered Potassium Titanium Niobate/Reduced Graphene Oxide Nanocomposite as a Potassium-Ion Battery Anode.

With graphite currently leading as the most viable anode for potassium-ion batteries (KIBs), other materials have been left relatively under-examined. Transition metal oxides are among these, with many positive attributes such as synthetic maturity, long-term cycling stability and fast redox kinetics. Therefore, to address this research deficiency we report herein a layered potassium titanium niobate KTiNbO5 (KTNO) and its rGO nanocomposite (KTNO/rGO) synthesised via solvothermal methods as a high-performance anode for KIBs. Through effective distribution across the electrically conductive rGO, the electrochemical performance of the KTNO nanoparticles was enhanced. The potassium storage performance of the KTNO/rGO was demonstrated by its first charge capacity of 128.1 mAh g-1 and reversible capacity of 97.5 mAh g-1 after 500 cycles at 20 mA g-1, retaining 76.1% of the initial capacity, with an exceptional rate performance of 54.2 mAh g-1 at 1 A g-1. Furthermore, to investigate the attributes of KTNO in-situ XRD was performed, indicating a low-strain material. Ex-situ X-ray photoelectron spectra further investigated the mechanism of charge storage, with the titanium showing greater redox reversibility than the niobium. This work suggests this low-strain nature is a highly advantageous property and well worth regarding KTNO as a promising anode for future high-performance KIBs.

Hybrid nanostructures for electrochemical potassium storage.

The wide availability and low cost of potassium resources have made electrochemical potassium storage a promising energy storage solution for sustainable decarbonisation. Research activities have been rapidly increasing in the last few years to investigate various potassium batteries such as K-ion batteries (KIBs), K-S batteries and K-Se batteries. The electrode materials of these battery technologies are being extensively studied to examine their suitability and performance, and the utilisation of hybrid nanostructures has undoubtedly contributed to the advancement of the performance. This review presents a timely summary of utilising hybrid nanostructures as battery electrodes to address the issues currently existing in potassium batteries via taking advantage of the compositional and structural diversity of hybrid nanostructures. The complex challenges in KIBs and K-S and K-Se batteries are outlined and the role of hybrid nanostructures is discussed in detail regarding the characteristics of intercalation, conversion and alloying reactions that take place to electrochemically store K in hybrid nanostructures, highlighting their multifunctionality in addressing the challenges. Finally, outlooks are given to stimulate new ideas and insights into the future development of hybrid nanostructures for electrochemical potassium storage.

A room temperature multivalent rechargeable iron ion battery with an ether based electrolyte: a new type of post-lithium ion battery.

The feasibility of developing a rechargeable iron ion battery is demonstrated for the first time. A rechargeable iron ion battery using mild steel as the anode and vanadium pentoxide as the cathode is demonstrated to deliver a specific capacity of 207 mA h g-1 at 30 mA g-1. Using ex situ characterisation techniques, reversible intercalation of iron ions into a host structure is confirmed.

Barium Titanate-Based Porous Ceramic Flexible Membrane as a Separator for Room-Temperature Sodium-Ion Battery.

Sodium-ion batteries (NIBs) are an alternative low-cost battery technology for large-scale energy storage application, and the development of high-performance polymer-based electrolytes is crucial for further advancement of low-cost NIBs. Though electrode materials provide significant contribution to the energy density of the battery, the separator plays a vital role in deciding the safety, duration, and performance of batteries. The glass fiber membrane is considered as the most compatible separator for NIBs because of its high ionic conductivity and reasonable performance. However, the leakage and flammability of the liquid electrolytes while using the glass fiber separator can lead to safety issues. Therefore, herein, we present an alternative approach for the first time to replace the glass fiber separator in NIBs using the porous ceramic membrane (PCM). The polymer blend-based PCM is prepared by a simple solution-casting technique and used as the separator in NIBs. The good thermal stability of the PCM up to 400 °C, high ionic conductivity of about 10-3 S cm-1, high electrolyte uptake, and porous nature make it a better choice over the glass fiber membrane. To demonstrate the applicability of PCM in NIBs, the sodium-ion storage property of hard carbon is evaluated using the PCM as the separator at room temperature. The specific capacity of hard carbon using the PCM-based separator is about 270 mA h g-1 at a current density of 30 mA g-1 which is ∼23% higher than the glass fiber separator (208 mA h g-1) at the same current density. The enhancement in specific capacity is due to the compatibility of the PCM with sodium electrodes, low interfacial resistance, high sodium-ion transference number (0.8), and good electrochemical stability (4.9 V) than the glass fiber separator. This study demonstrates a promising alternative separator to the glass fiber membrane, which can lead to the development of a practical and safe NIB.

Enhanced Sodium Ion Storage in Interlayer Expanded Multiwall Carbon Nanotubes.

We report an effective approach of utilizing multiwalled carbon nanotubes (MWCNTs) as an active anode material in sodium ion batteries by expanding the interlayer distance in a few outer layers of multiwalled carbon nanotubes. The performance enhancement was investigated using a density functional tight binding (DFTB) molecular dynamics simulation. It is found that a sodium atom forms a stable bonding with the partially expanded MWCNT (PECNT) with the binding energy of -1.50 eV based on the density functional theory calculation with van der Waals correction, where a sodium atom is caged between the two carbon hexagons in the two consecutive MWCNTs. Wave function and charge density analyses show that this binding is physisorption in nature. This larger exothermic nature of binding energy favors the stable bonding between the PECNT and a sodium atom, and thereby, it helps to enhance the electrochemical performance. In the experimental works, partial opening of the MWCNT with the expanded interlayer has been designed by the well-known Hummer's method. It has been found that the introduction of functional groups causes a partial opening of the outer few layers of a MWCNT, with the inner core remaining undisturbed. The enhanced performance is due to an expanded interlayer of carbon nanotubes, which provide sufficient active sites for the sodium ions to adsorb as well as to intercalate into the carbon structure. The PECNT shows a high specific capacity of 510 mAh g-1 at a current density of 20 mA g-1, which is about 2.3 times the specific capacity obtained for a pristine MWCNT at the same current density. This specific capacity is higher when compared to other carbon-based materials. The PECNT also shows a satisfactory cyclic stability at a current density of 200 mA g-1 for 100 cycles. Based on our experimental and theoretical results, an alternative perspective for the storage of sodium ions in MWCNTs is proposed.