Rechargeable Seawater Batteries Research Articles

A Membrane-Free Rechargeable Seawater Battery Unlocked by Lattice Engineering.

Seawater batteries that directly utilize natural seawater as electrolytes are ideal sustainable aqueous devices with high safety, exceedingly low cost, and environmental friendliness. However, the present seawater batteries are either primary batteries or rechargeable half-seawater/half-nonaqueous batteries because of the lack of suitable anode working in seawater. Here, a unique lattice engineering to unlock the electrochemically inert anatase TiO2 anode to be highly active for the reversible uptake of multiple cations (Na+, Mg2+, and Ca2+) in aqueous electrolytes is demonstrated. Density functional theory calculationsfurther reveal the origin of the unprecedented charge storage behaviors, which can be attributed to the significant reduction of the cations diffusion barrier within the lattice, i.e., from 1.5 to 0.4eV. As a result, the capacities of anatase TiO2 with 2.4% lattice expansion are ≈100 times higher than the routine one in natural seawater, and ≈200 times higher in aqueous Na+ electrolyte. The finding will significantly advance aqueous seawater energy storage devices closer to practical applications.

Influence of organic matter on seawater battery desalination performance

A rechargeable seawater battery desalination (SWB-D) system stores energy in a battery cell while removing salts from saline water via a sodium superionic conductor membrane and an anion exchange membrane. However, the electrochemical performance often degrades owing to the organic fouling generated on the ion exchange membranes. In this study, we investigated the fouling behavior of the SWB-D system by individually dissolving three different types of organic matter—humic acid, sodium alginate, and bovine-serum-albumin. In terms of the salt-removal performance of the SWB-D system, gradual degradation was observed over three charging cycles using hydrophobic humic acid (~13 %) and bovine-serum-albumin (~18 %), whereas no degradation was caused by hydrophilic sodium alginate. Continuous water flow mitigated the fouling behavior, and a large volume of saline water enabled longer charging. The increase in the electrical resistance of the SWB-D system was measured in the presence of organic matter using electrochemical impedance spectroscopy and the four-electrode method. Additionally, the presence of fouling layer was identified using field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, and Fourier-transform infrared spectrometry. In conclusion, the results demonstrated that the hydrophobic organic matter in the feed water could be unfavorable when operating the SWB-D system.

Rechargeable Seawater Batteries Based on Polyimide Anodes

Being nearly unlimited natural resource containing mostly Na cations, the use of seawater as an electrolyte solution (aka seawater batteries) for electrochemical energy storage has received growing attention. To date, the vast majority of studies have focused on the use of seawater in Na-metal batteries protected by ion-conductive membranes hermetic to water. These systems, however, are complex and expensive, and suffer from a short cycling life. Here, we present alternative seawater batteries that utilize polyimide anodes. With its high capacity of more than 140 mAh/g, impressive rate capability, and excellent long-term stability (98% capacity retention after more than 9000 cycles), the prepared polyimide electrodes demonstrated to be promising candidate anodes for seawater electrochemical energy storage devices. Looking for a suitable cathode, we explored the use of nickel hexacyanoferrate (Ni-HCF) and activated carbon. Our findings suggest an innovative approach to design sustainable and cost-effective systems for large-scale energy storage.

Recent Advances in Solar Rechargeable Seawater Batteries Based on Semiconductor Photoelectrodes.

With the ever-increasing demand for energy in the world, the tendency to use renewable energies has been growing rapidly. Sunlight, as an inexhaustible energy source, and the oceans, as one of the most valuable treasures on Earth, are available for free. Simultaneous exploitation of these two sources of energy and matter (sunlight and oceans) in one configuration can provide a sustainable solution for future energy supply. Among the various types of such energy storage and conversion systems, solar rechargeable seawater batteries (SRSBs) can meet this need by storing the chemical energy of seawater by receiving solar energy. SRSBs consist of two compartments: a closed compartment including a sodium metal anode in an organic liquid electrolyte, and an open compartment containing a semiconductor photoelectrode immersed in seawater, which are separated from each other by a ceramic solid electrolyte membrane. In this complex system, the photoelectrode is irradiated by sunlight, whereby electrons are excited and reach the Na metal anode after passing though the external circuit. The ceramic solid electrolyte harvests only sodium ions from seawater and transfers them to the anodic part, where the transferred ions are reduced to sodium metal atoms. At the same time, an oxygen evolution reaction takes place at the cathodic part. In this way, the battery is charged. The use of a photoelectrode in the charging process significantly increases the voltage efficiency of SRSBs to more than 90%, whereas a cell with only the seawater compartment (without a photoelectrode) will not deliver satisfactory performance. Therefore, to achieve very high efficiencies, designing an accurate system with the best components is absolutely necessary. This review focuses on the working principle of SRSBs, at the same time explaining the effect of key components on the performance and stability of SRSBs. The role of the semiconductor photoelectrode in improving the voltage efficiency of SRSBs is also described in detail, and finally strategies proposed to overcome obstacles to the commercialization of SRSBs are introduced.

Development of Rechargeable Seawater Battery Module

Rechargeable seawater batteries (SWBs) use Na+ ions dissolved in water (seawater or salt-water) as the cathode material. They are attracting attention for marine applications such as light buoys, marine drones, auxiliary power for sailing boats and so on. So far, SWB design has been developed from the coin-type to prismatic-shape cell for research purposes to investigate cell components and electrochemical behaviors. However, for commercial applications, that generally require >12 V and >15 W, the development of an SWB module is required, including cell assembly and packing design. The purpose of this work was to conduct research on the SWB cell assembly method while considering the SWB’s properties and minimizing current imbalance. Additionally, a 5 Series (S) 4 Parallel (P) SWB module is constructed and validated using commercially available light buoys (12 V, 15 W).

Near surface electric field enhancement: Pyridinic-N rich few-layer graphene encapsulating cobalt catalysts as highly active and stable bifunctional ORR/OER catalyst for seawater batteries

Rechargeable seawater batteries (SWBs) are recently considered as a new approach in next-generation energy storage. However, the presence of chloride ions inhibits the performance and durability of the air cathode electrocatalysts. This study is the first research to report the effect of the built-in electric field on corrosion prevention via Cl- repulsion. Our DFT model successfully demonstrated the near-surface charge transfer at the interface of cobalt core and pyridinic-N graphene (Co (fcc)/N-Gr) strongly contributed to advanced catalytic activity and selectively Cl- repulsion in seawater electrolyte. Experimentally, the structure of a few layered N-doped graphene encapsulated cobalt (Co 4 mmol-N/C) showed superior catalytic activity in both alkaline (ΔE (Ej=10 − E1/2) = 0.774 V) and seawater (ΔE = 1.167 V). Furthermore, Co 4 mmol-N/C demonstrated an extremely low overpotential (0.56 V) at 0.1 mA and presented superior stability for 100 h in a rechargeable SWB.

Development of Prismatic Cells for Rechargeable Seawater Batteries

AbstractRechargeable seawater batteries (SWBs) using seawater as a catholyte have attracted extensive attention owing to the ocean's high theoretical energy density (3051 Wh L‐1, 3145 Wh kg‐1) and excellent thermal management. However, despite many improvements in materials and cell designs used in SWBs so far, there is a limit on the energy density in practical use, because of the lack of optimization of the cell structure. Herein, this work introduces a novel design by applying a rigid frame with an extended space called “prismatic‐type.” Consequently, an energy density of 23 Wh (242 Wh L‐1) is obtained by increasing the specific area of the unit cell and the capability of the anode active materials in the internal space. In addition, it enables the design of a discrete type that can improve the power density by increasing the surface area of the cathode current collectors. With the increased surface area, a peak power of 1162 mW is achieved for the discrete type compared to 727 mW for the integral type. These results suggest that these newly designed prismatic SWBs could contribute to practical applications in the near future.

A Na+ ion-selective desalination system utilizing a NASICON ceramic membrane

Seawater is a virtually unlimited source of minerals and water. Hence, electrodialysis (ED) is an attractive route for selective seawater desalination due to the selectivity of its ion exchange membrane (IEM) toward the target ion. However, a solution-like IEM, which is permeable to water and ions other than the target ion, results in the leakage of water as well as extraction of unwanted ions. This degrades the productivity and purity of the system. In this study, A novel desalination system was developed by replacing the cation exchange membrane (CEM) with a Na super ionic conductor (NASICON) in ED. NASICON exceptionally permits Na+ ion migration, and this enhanced the productivity of desalted water by removing 98% of Na+ while retaining water and other cationic minerals. Therefore, the final volume of desalted water in N-ED was 1.36 times larger compared to that of ED. In addition, the specific energy consumption for salt (NaCl) extraction was reduced by ∼13%. Furthermore, the NASICON in N-ED was replaced into a two-sided NASICON-structured rechargeable seawater battery, thereby further conserving ∼20% energy by simultaneously coupling selective desalination with energy storage. Our findings have positive implications and further optimizations of the NASICON will enable practical and energy-effective applications for seawater utilization.

Simultaneous Energy Storage and Seawater Desalination using Rechargeable Seawater Battery: Feasibility and Future Directions.

Rechargeable seawater battery (SWB) is a unique energy storage system that can directly transform seawater into renewable energy. Placing a desalination compartment between SWB anode and cathode (denoted as seawater battery desalination; SWB‐D) enables seawater desalination while charging SWB. Since seawater desalination is a mature technology, primarily occupied by membrane‐based processes such as reverse osmosis (RO), the energy cost has to be considered for alternative desalination technologies. So far, the feasibility of the SWB‐D system based on the unit cost per desalinated water ($ m−3) has been insufficiently discussed. Therefore, this perspective aims to provide this information and offer future research directions based on the detailed cost analysis. Based on the calculations, the current SWB‐D system is expected to have an equipment cost of ≈1.02 $ m−3 (lower than 0.60–1.20 $ m−3 of RO), when 96% of the energy is recovered and stable performance for 1000 cycles is achieved. The anion exchange membrane (AEM) and separator contributes greatly to the material cost occupying 50% and 41% of the total cost, respectively. Therefore, future studies focusing on creating low cost AEMs and separators will pave the way for the large‐scale application of SWB‐D.

Redox chemistry of advanced functional material for low-cost and environment-friendly seawater energy storage

Although rechargeable seawater batteries are promising energy storage systems, their electrochemical performance is inferior to that of lithium batteries; moreover, opportunities for improving their performance are restricted by the limited range of available anode materials to complement seawater cathodes. Organic redox materials can help overcome the drawbacks associated with seawater batteries because of their inherent fast charge transfer capability. Therefore, in this study, we design a unique hybrid seawater battery in which poly (4-styrenesulfonate) as a sodium-ion storage polymer is functionalized with hard carbon (HC) to form a functional anode with high capacity by in situ polymerization. Sodium-ion storage mechanisms of the poly (4-styrenesulfonate) (PSS) and HC-PSS functional material are investigated through electron spin resonance, solid nuclear magnetic resonance, X-ray photoelectron spectroscopy, and molecular orbital studies. Each HC and PSS in the HC-PSS electrode clearly contribute to reversible electrochemical reactions. This polymer is observed to prevent the growth of a solid electrolyte interface on the surface of the functionalized HC-PSS anode, and the seawater battery exhibits excellent electrochemical properties, making it suitable for high-performance eco-friendly energy storage systems.

Seawater Batteries: Design of Large‐Scale Rectangular Cells for Rechargeable Seawater Batteries (Adv. Sustainable Syst. 1/2021)

Seawater Batteries: Design of Large‐Scale Rectangular Cells for Rechargeable Seawater Batteries (Adv. Sustainable Syst. 1/2021)

Synthesis and Characterization of Von Alpen-Type Nasicon Ceramic and Its Application to Rechargeable Seawater Battery

Rechargeable seawater battery (SWB), which utilizes naturally abundant seawater as its cathode, is having attention for a next-generation large-scale energy storage system (ESS) due to its low cost and eco-friendliness. For an effective Na+ transfer solid electrolyte for SWB, Hong-type NASICON (Na3Zr2Si2PO12) ceramic has been used because of its known high Na-ion conductivity (~3x10-4 S/cm). However, the SWB coin cell test showed that the Hong-type NASICON ceramic accounts for 62% (132Ω) of the total cell resistance (214 Ω). This has been considered as one of major drawbacks for developments of SWB technology. Hence, it has been requested to achieve higher ionic conductivity of Na-ion conducting ceramics, increasing power of the current SWB by reducing its cell ohmic resistance.In this talk, von Alpen-type NASICON (Na3.3Zr1.55Si0.7P1.3O11) ceramic was synthesized by solid-state reaction and was observed to have ~1.0x10-3S/cm of Na-ion conductivity, which three times higher than that of Hong-type one. It was found that the von Alpen-type NASICON has more rhombohedral phases with a bigger grain size (2~6μm) compared to the major phases of Hong-type one, and additionally less secondary phases of ZrO2 were observed in the von Alpen-type NASICON. These differences were believed to be major reasons for higher Na-ion conductivity observed in von Alpen-type NASICON ceramic. These structural characteristics were also found to led to a stronger mechanical strength (50MPa) of the von Alpen-type NASICON rather than that (20MPa) of Hong-type one, which enables us to have thinner thickness (~0.5mm) of the ceramic solid electrolyte at the present work.With the use of von Alpen-type NASICON having a higher Na-ion conductivity and thinner thickness in SWB coin cell, it shows 96% of the power increased (to 9.8 mW/cm2 from 5.1 mW/cm2 of the cell using Hong-type ceramic). More details will be reported in the talk.

A Simple Synthesis Method of Single-Size AgCl Nano-Particles and Its Discharge Behavior

Single-size AgCl nanoparticles were successfully synthesized through a direct precipitation method with ethylene diamine tetraacetic acid (EDTA) as the complexant. Fourier transform infra-Red (FTIR), X-ray diffraction (XRD), scanning electron micro spectroscopy (SEM) and density functional theory (DFT) calculation were conducted to analyze the structure and morphology. Linear sweep voltammetry and cyclic voltammetry (CV) were used to evaluate the electrochemical activity. The kind of formed complexes between Ag+ and EDTA in the solutions changes by varying pH values in the solution. The stability of the formed complexes differs from each other, which notably affects the nucleation and growth of AgCl particles in the solutions and subsequently the particle size and morphology of synthesized AgCl particles. The reactants concentration, temperature and CAg+/CEDTA ratio are also dominant to the particle size and morphology of synthesized AgCl particles. Single-size AgCl nanoparticles (75 nm) with spherical shape were synthesized. The AgCl electrodes prepared by synthesized AgCl nanoparticles show the highest current density of 15.2 mA/cm2 at potential −0.2 V and excellent cathodic and anodic recycling properties, indicating that the AgCl electrode is suitable for use as the electrode for rechargeable seawater battery.

Compartmentalized desalination and salination by high energy density desalination seawater battery

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.

Design of Large‐Scale Rectangular Cells for Rechargeable Seawater Batteries

AbstractRechargeable 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.

Energy projection of the seawater battery desalination system using the reverse osmosis system analysis model

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.

Redox-Active Functional Electrolyte for High-Performance Seawater Batteries.

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.

Hybridization of cathode electrochemistry in a rechargeable seawater battery: Toward performance enhancement

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 g−1) 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 cm−2) compared to those of the SWB operated with lower surface area carbon felt (2.2 m2 g−1, 1.24 V, 71%, and 5.5 mW cm−2, respectively). These findings suggest that hybridization of the EDL and OER/ORR processes on the cathode side of SWB can improve overall performance.

Hybrid photoelectrochemical-rechargeable seawater battery for efficient solar energy storage systems

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.

The Chemical Stability of Nasicon As a Solid Electrolyte for Seawater Batteries

Seawater batteries have attracted significant attention for use as grid-scale energy storage systems (ESSs) due to the effective utilization of abundant resources of seawater as a catholyte. Sodium ions in seawater selectively transfer through a solid electrolyte to the anode for saving the chemical energy. For the selective transfer of sodium ions, NASICON (Na3Zr2Si2PO12) electrolytes are one of the suitable candidates for the solid electrolyte to prevent a short circuit between the catholyte and anode. However, NASICON powder is known to be dissolved in water because of the structural instability, leading to catastrophic failure of the system, while NASICON solid electrolytes are stable in seawater during the battery operation. In this regard, we have carefully compared the stability of NASICON powder and pellets in both DI water and seawater associated with different degradation mechanism. Figure shows the structural stability of NASICON pellets after the immersion tests in DI water and seawater indicative of the chemical stability of NASICON in seawater. In addition, the electrochemical performance shows higher stability of the seawater-immersed electrolyte than the DI water-immersed electrolyte. The corresponding analyses are carried out to confirm the effect of the investigation. Furthermore, we have employed polymer coating methods to enhance stability and performance as a seawater battery system. The coating layer enables to prevent direct contact with seawater, resulting in longer stability during operation without compromising ionic conductivity. These results reveal that NASICON solid electrolytes can be operated in seawater with high stability and performance. Figure. The chemical stability comparison of NASICON in seawater and DI water References Mauvy, F., Siebert, E., & Fabry, P. (1999). Reactivity of NASICON with water and interpretation of the detection limit of a NASICON based Na+ion selective electrode. Talanta , 48(2), 293–303.Fuentes, R. O., Figueiredo, F., Marques, F. M. B., & Franco, J. I. (2001). Reaction of NASICON with water, Solid State Ionics , 263, 309–314.Kim, Y., Kim, H., Park, S., Seo, I., & Kim, Y. (2016). Na ion- Conducting Ceramic as Solid Electrolyte for Rechargeable Seawater Batteries. Electrochimica Acta , 191, 1–7.Jung, J. Il, Kim, D., Kim, H., Jo, Y. N., Park, J. S., & Kim, Y. (2017). Progressive Assessment on the Decomposition Reaction of Na Superionic Conducting Ceramics. ACS Applied Materials & Interfaces , 9(1), 304–310. Figure 1