Journal of Materials Chemistry A, J. Mater. Chem. A, 2020, 8, 21804-21811 (Website link)

Understanding the interfacial reaction between a solid electrolyte and reactive species is of vital importance for the development of various battery systems. In particular, the interaction between the solid electrolyte, aqueous media, and dissolved gaseous phases at catalysts affects reaction kinetics and hybrid battery performance. These effects are concentrated at the interfaces that the three kinetic fluxes simultaneously encounter, which we refer to as a “triple-flux interface (TFI)”. The TFI consists of a Na+ super ionic conductor as a solid electrolyte, a seawater catholyte, and dissolved gaseous phases on a catalytic carbon felt. Here, we provide insights into the interfacial dynamics during the operation of a hybrid Na-seawater battery under harsh operating conditions, including at high current densities and in acidified seawater solutions. We discover that high current densities and the permeation of acid compounds during the charge process cause the irreversible extraction of Na+, crevasse-like brokenness, and unavoidable phase distortion from the surface that is in contact with seawater. The investigation of the factors in terms of chemical potentials of the charge carriers would provide insight into designs for high-powered seawater battery systems.

ACS Applied Materials & Interfaces, ACS Appl. Mater. Interfaces 2020, 12, 29, 32689–32697 (Website link)

Although development and utilization of efficient catalysts with earth-abundant and cheap elements are desired, precious noble metal-based catalysts are still widely used and studied due to the urgent need to address energy and environmental issues. Polyoxometalates (POMs) can be excellent candidates in this context. In this study, we found that oxo-bridged tetraruthenium polyoxometalate (RuPOM) exhibits excellent electrocatalytic activity for both oxygen evolution and reduction reactions (OER and ORR) with minimal use of noble metal elements and can be used for the development of efficient seawater batteries (SWBs). The deposition of RuPOM on a desired electrode with conducting carbon Ketjen black (KB) by the simple slurry coating method imparted bifunctional OER/ORR activity to the underlying electrode. Although the mass activity was similar, RuPOM/KB mixtures exhibited superior activity even compared to commercially available Pt/C when comparing the activity per noble metal element. Based on these findings, we employed RuPOM to develop efficient SWBs. RuPOM significantly lowered the charging potential and increased the discharging potential of SWBs, which are related to OER and ORR, respectively. This study can provide insights into the development of POM-based electrocatalysts and their application in energy storage and conversion devices.

Advanced Sustainable Systems, Adv. Sustainable Syst. 2020, 2000106 (Website link)

Rechargeable seawater batteries (SWBs) are regarded as sustainable alternatives to Li‐ion batteries due to the use of an unlimited and free source of Na ion active materials. Although many approaches including the introduction of new catalysts have successfully improved the performance of SWBs, reconsidering the cell design is an urgent requirement to improve the performance and scale up the production of practical batteries. In this study, by adjusting the maximum space efficiency, a rectangular cell is developed which due to its unique architecture, benefits from optimized contact to improve the overall charge transfer in the system. In view of the rigidity of the solid electrolyte, the novel cell model is intended to have adequate flexibility to be easily transported and practically utilized. Furthermore, the enhanced efficiency of the parallel stacked modules, indicates the capability of this cell in practical use. The designed catalyst‐free cell system shows a record capacity of 3.8 Ah (47.5 Ah kg−1), energy of 11 Wh (137.5 Wh kg−1), and peak power of 523 mW for individual unit cell, while it also retains performance up to 100 cycles. This design paves the way for commercializing rechargeable seawater batteries.

Journal of Materials Chemistry A, J. Mater. Chem. A, 2020, 8, 17980 (Website link)

The organic polymer battery is a promising alternative to the lithium ion battery, however its various properties need to be improved. In this study, we demonstrate an advanced organic radical battery (ORB) using a cathode based on poly(2,2,6,6-tetramethylpiperidine-4-yl-1-oxyl vinyl ether) (PTVE) and a microporous gel polymer electrolyte based on electrospun polyimide membrane. To improve upon the low electrical conductivity of PTVE, it is functionalized on carbon nanotubes (CNTs) by a dissolution–diffusion process. The PTVE-functionalized CNTs have a π–π* interaction between the two components, and could be formed into a dense electrode with reasonable porosity. The gel polymer electrolyte with the desired microporosity is also highly compatible. As a result, Na-ion organic full cells using the PTVE–CNT composite electrode, gel polymer electrolyte, and hard carbon anode show good rate capability and stable cycling. The battery achieves discharging capacities of 128.6 and 68.2 mA h g−1 at 0.5C and 10C with 100% coulombic efficiency and no self-discharge. Hence, this combination of composite electrode and gel polymer electrolyte leads to a safe, lightweight, and environmentally benign sodium battery with high power-rate capability for various applications.

Advanced Functional Materials, Adv. Funct. Mater. 2020, 2005362 (Website link)

This paper describes a new, high-performance, Pb-based nanocomposite anode material for lithium-ion batteries. A unique nanocomposite structure of Pb@PbO core-shell nanoparticles in a carbon matrix is obtained by using a simple high-energy ball milling method using the low-cost starting materials PbO and carbon black. Electrochemical performance tests show its excellent reversible capacity (≈600 mAh g−1) and cycle stability (92% retention at 100th cycle), which are one of the best values reported for Pb-based anodes in the literature. Synchrotron X-ray diffraction and absorption techniques revealed the detailed lithium storage mechanism that can be highlighted with the unexpectedly wide reversible Pb redox range (between Pb2+ and Pb4−) and the evolution of Zintl-type LiyPb structures during the electrochemical lithium reaction. The results provide new insights into the lithium storage mechanism of these Pb-based materials and their potential as low-cost, high-performance anodes.

Desalination, Desalination 495 (2020) 114666 (Website link)

A novel desalination seawater battery (DSWB) has been developed by adapting the design of a rechargeable seawater battery, which operates for both seawater desalination and energy storage. The DSWB system has a unique architecture composed of two subsystems used for desalination and salination during charging and discharging, respectively. A higher energy density (4010 Wh/kg) can be achieved at high nominal cell potential (EO = 3.46 V, pH 8.4) in the DSWB system throughout the charging (desalination) process which is much larger than those of any reported desalination battery system (< 78 Wh/kg and <1.25 V). In addition, the system provides a compartment for desalination, which is independent from the salination (discharging) process, enabling the salination process to be carried out without renewing the seawater for every step, which enables the proposed system to achieve high levels of seawater desalination (up to 84%). The results affirm that further optimization of the cell system will facilitate economical and practical desalination battery applications with high energy density.

Journal of Materials Chemistry A, J. Mater. Chem. A, 2020,8, 14528-14537 (Website link)

In a conventional Na-ion battery system using liquid electrolyte, there are critical safety issues due to the instability of the liquid electrolyte. Na3Zr2Si2PO12 (NASICON) solid electrolyte is a material that is sufficient to replace a liquid electrolyte as it has high ionic conductivity and thermal and electrochemical stability. However, as there is a large interfacial resistance in the NASICON solid electrolyte powder, even when used in combination with a polymer electrolyte, the advantageous effects of ceramics are not easily exhibited. In this study, we propose a top-down method of combining a polymer with a ceramic in which an ion transport channel is previously formed. In this method, a NASICON solid electrolyte is partially sintered to form ion transport channels. Then the NASICON solid electrolyte pores are filled with an epoxy polymer to increase the strength of the epoxy-NASICON composite electrolyte. This method demonstrates the possibility of our composite electrolyte being used as a thin and strong film. As a result of our methods, the ionic conductivity and thermal and electrochemical stability of NASICON were maintained, while the physical strength was enhanced by approximately 2 times. In addition, a capacity of 120 mA h g−1 and stability of 20 cycles were confirmed in a half cell with a Na3V2(PO4)3 cathode and Na metal. This method proposes a new direction for research regarding composite electrolytes created using an oxide-based solid electrolyte.

Advanced Functional Materials, Adv. Funct. Mater. 2020, 202002008 (Website link)

Concerning the safety aspects of Li+ ion batteries, an epoxy-reinforced thin ceramic film (ERTCF) is prepared by firing and sintering a slurry-casted composite powder film. The ERTCF is composed of Li+ ion conduction channels and is made of high amounts of sintered ceramic Li1+xTi2−xAlx(PO4)3 (LATP) and epoxy polymer with enhanced mechanical properties for solid-state batteries. The 2D and 3D characterizations are conducted not only for showing continuous Li+ ion channels thorough LATP ceramic channels with over 10^−4 S cm−1 of ionic conductivity but also to investigate small amounts of epoxy polymer with enhanced mechanical properties. Solid-state Li+ ion cells are fabricated using the ERTCF and they show initial charge–discharge capacities of 139/133 mAh g−1. Furthermore, the scope of the ERTCF is expanded to high-voltage (>8 V) solid-state Li+ ion batteries through a bipolar stacked cell design. Hence, it is expected that the present investigation will significantly contribute in the preparation of the next generation reinforced thin ceramic film electrolytes for high-voltage solid-state batteries

Chemical Engineering Journal, Chemical Engineering Journal 395 (2020) 12508 (Website link)

Water-stressed countries have been shifting their sources of clean water from inland freshwater to seawater. This led to a comprehensive exploration of seawater desalination processes to address water scarcity; however, membrane processes have expensive operational costs and high energy consumption. In this regard, this study presented a novel energy self-sufficient desalination system design that incorporates rechargeable seawater batteries as an additional energy storage system. Experimental data were projected using the reverse osmosis system analysis model to determine the configuration that achieved the lowest energy consumption and highest charging rate. The results show that the seawater battery achieved a satisfactory desalination performance with >90% and 74%−82% removal of sodium and chloride ions from actual water samples, respectively. Among the configurations, using ultrafiltration as pretreatment and applying 1.8 mA as initial current yielded the lowest energy consumption (1.35 kWh/m3) and the highest energy charging rate (1.01). Compared to the conventional reverse osmosis desalination plants (2.83 kWh/m3), the seawater battery-desalination system has a huge potential in addressing the major disadvantages of current desalination technologies.

Journal of Materials Chemistry A, (Website link)

Rechargeable seawater batteries (SWBs) have recently been investigated as a potential candidate for future energy storage systems, owing to their cost-effectiveness and environmentally friendly properties derived from the use of naturally abundant seawater as a catholyte. However, the fundamental understanding of the cathode reactions in SWBs is not yet fully elucidated; hence, an investigation of their mechanisms is imperative for future development. Herein, parasitic cathode reactions other than the previously identified oxygen evolution/reduction reactions (OERs/ORRs) are identified for the first time using activated carbon cloth (ACC) as the cathode current collector. In this study, carbon fibers of the current collector were observed to undergo cathode side-reactions such as fiber-fracturing carbon corrosion during charging and surface-insulating CaCO3 precipitation via carbon dioxide capture during discharging, both resulting in cathode performance failure. Moreover, carbon corrosion was determined to be the dominant factor behind performance degradation under normal charge–discharge cycling conditions in comparison to CaCO3 precipitation, which was found to be a reversible phenomenon during the operation of the SWB. These results provide insight for future work into enhancing the longevity of SWBs by identifying carbon corrosion as the main cathode performance degradation mechanism.

Advanced Functional Materials, (Website link)

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.

ChemSusChem, (Website link)

Rechargeable seawater batteries have gained recognition as key sustainable electrochemical systems by employing the near-infinite and eco-friendly catholyte seawater. However, their practical applications have been limited owing to the low chemical and electrochemical stability of the anode component. Herein, a stability-secured approach was developed by using sodium-biphenyl-dimethoxyethane solution as a redox-active functional anolyte for high-performance seawater batteries. This anolyte system shows high electrochemical stability, superior cycle performance, and cost-effectiveness over conventional electrolyte systems.

Electrochimica Acta, (Website link)

Eco-friendly harnessing of both ocean chemical energy and solar energy would represent a sustainable solution for future energy conversion/storage systems, but it has been challenging to enhance the energy efficiency of such systems for practical applications. Here, we demonstrate an efficient photoelectrochemical-assisted rechargeable seawater battery. By integrating TiO2 nanostructure-based photoelectrodes with the seawater battery, we achieved significant enhancement of the voltage efficiency during the charging/discharging processes; effective photocharging with the TiO2 photoanode reduced the charging voltage to ~2.65 V, while the heated carbon felt (HCF) cathode in the seawater battery exhibited charging/discharging voltages of ~3.8 V and ~2.9 V, respectively. Such a charging voltage reduction led to a voltage efficiency of ~109%. Moreover, interestingly, we found that TiO2 nanostructures showed excellent photoelectrochemical performances in seawater in association with the efficient photocharging. As a result, the utilization of TiO2 nanostructures as photocharging/discharging electrodes provides a feasible strategy to optimize the cell configuration for highly efficient solar seawater batteries.

Journal of Power Sources, Volume 450, 29 February 2020, 227600 (Website link)

Seawater batteries (SWBs) are promising energy storage systems for the future because of their eco-friendly utilization of abundant seawater as low-cost sources of Na ion active cathode materials. However, the overall efficiency (i.e. voltage and/or energy efficiency) and power performance of SWBs are limited by the sluggish kinetics of the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) on the current collector of the SWB cathode. Generally, the charge storage and delivery process through the electric double layer (EDL) are much faster compared to OER/ORR and other Faradic reactions. To improve the performance of SWBs, we utilized the benefit of EDL formation along with OER/ORR activities using commercial high surface area (~2038 m2 g1) and hydrophilic activated carbon cloth (ACC) as a current collector at the cathode. As anticipated, the SWB with ACC showed a reduced voltage gap (0.49 V), high energy efficiency (86%), improved rate capability, and improved power performance (16.2 mW cm2) compared to those of the SWB operated with lower surface area carbon felt (2.2 m2 g1, 1.24 V, 71%, and 5.5 mW cm2, respectively). These findings suggest that hy-bridization of the EDL and OER/ORR processes on the cathode side of SWB can improve overall performance.