Na-air Batteries Research Articles

In situ ambient pressure x-ray photoelectron spectroscopy study on O2/H2O-assisted Na–CO2 batteries

Na–CO2 battery is considered a high-energy-density storage system with the ability to utilize CO2. However, unlike its Li counterpart, it suffers from an unclear reaction mechanism and poor battery performance. CO2 is an inert species and requires high activation energy. Moreover, the understanding of how additives such as O2 and H2O aid the cathode reaction remains lacking. Herein, the mechanism of the CO2 reduction reaction is unraveled through in situ ambient pressure X-ray photoelectron spectroscopy (APXPS). The oxidation states of the discharged products can be well revealed to understand the reactions. Unlike previous studies, a pure CO2 environment was found to have poor electrochemical activity. When additives, such as O2 and H2O, were introduced to the system, some Csp2 was formed. We propose that Csp2 should be attributed to the alkene formation as the decomposition product of ionic liquid, which serves as the electrolyte. The formation of elemental carbon as the discharge product is unlikely, which is in stark contrast to previous studies. As a result, the poor electrochemical activity of the pure CO2 system leads to the formation of CO, which escapes from the electrode surface and results in poor reversibility. Additives such as O2 and H2O are electrochemically active themselves, while CO2 participated in the reaction chemically, reducing the chemical reversibility. Therefore, a system without CO2 is more beneficial to the Na–air batteries.

Activating reversible carbonate reactions in Nasicon solid electrolyte-based Na-air battery via in-situ formed catholyte

Out of practicality, ambient air rather than oxygen is preferred as a fuel in electrochemical systems, but CO2 and H2O present in air cause severe irreversible reactions, such as the formation of carbonates and hydroxides, which typically degrades performance. Herein, we report on a Na-air battery enabled by a reversible carbonate reaction (Na2CO3·xH2O, x = 0 or 1) in Nasicon solid electrolyte (Na3Zr2Si2PO12) that delivers a much higher discharge potential of 3.4 V than other metal-air batteries resulting in high energy density and achieves > 86 % energy efficiency at 0.1 mA cm−2 over 100 cycles. This cell design takes advantage of moisture in ambient air to form an in-situ catholyte via the deliquescent property of NaOH. As a result, not only reversible electrochemical reaction of Na2CO3·xH2O is activated but also its kinetics is facilitated. Our results demonstrate the reversible use of free ambient air as a fuel, enabled by the reversible electrochemical reaction of carbonates with a solid electrolyte.

Low-Overpotential Rechargeable Na-CO2 Batteries Enabled by an Oxygen-Vacancy-Rich Cobalt Oxide Catalyst.

Rechargeable sodium-carbon dioxide (Na-CO2) batteries have been proposed as a promising CO2 utilization technique, which could realize CO2 reduction and generate electricity at the same time. They suffer, however, from several daunting problems, including sluggish CO2 reduction and evolution kinetics, large polarization, and poor cycling stability. In this study, a rambutan-like Co3O4 hollow sphere catalyst with abundant oxygen vacancies was synthesized and employed as an air cathode for Na-CO2 batteries. Density functional theory calculations reveal that the abundant oxygen vacancies on Co3O4 possess superior CO2 binding capability, accelerating CO2 electroreduction, and thereby improving the discharge capacity. In addition, the oxygen vacancies also contribute to decrease the CO2 decomposition free energy barrier, which is beneficial for reducing the overpotential further and improving round-trip efficiency. Benefiting from the excellent catalytic ability of rambutan-like Co3O4 hollow spheres with abundant oxygen vacancies, the fabricated Na-CO2 batteries exhibit extraordinary electrochemical performance with a large discharge capacity of 8371.3 mA h g-1, a small overpotential of 1.53 V at a current density of 50 mA g-1, and good cycling stability over 85 cycles. These results provide new insights into the rational design of air cathode catalysts to accelerate practical applications of rechargeable Na-CO2 batteries and potentially Na-air batteries.

Intrinsic Properties Affecting the Catalytic Activity toward Oxygen Reduction Reaction of Nanostructured Transition Metal Nitrides as Catalysts for Hybrid Na-Air Batteries

Nanostructured transition metal nitrides (TMNs) have been considered as a promising substitute for precious metal catalysts toward ORR due to their multi-electron orbitals, metallic properties, and low cost. To design TMN catalysts with high catalytic activity toward ORR, the intrinsic features of the influencing factor on the catalytic activity toward ORR of nanostructured TMNs need to be investigated. In this paper, titanium nitride (TiN), zirconium nitride (ZrN), and hafnium nitride (HfN) nanoparticles (NPs) are highly efficient and synthesized in one step by the direct current arc plasma. TiN, ZrN, and HfN NPs with an oxidation layer are applied as the catalysts of hybrid sodium–air batteries (HSABs). The effect of the composition and structural attributes of TMNs on ORR catalysis is defined as follows: (i) composition effect. With the increase in the oxygen content, the catalytic ORR capability of TMNs decreases progressively due to the reduction in oxygen adsorption capacity; (ii) structure effect. The redistribution of the density of states (DOS) of ZrN indicates higher ORR activity than TiN and HfN. HSABs with ZrN exhibit an excellent cyclic stability up to 137 cycles (about 140 h), an outstanding rate performance, and a specific capacity of 2817 mAh·g−1 at 1.0 mA·cm−2.

Gel Adsorbed Redox Mediators Tempo as Integrated Solid‐State Cathode for Ultra‐Long Life Quasi‐Solid‐State Na–Air Battery

AbstractIn metal–air batteries, the integrated solid‐state cathode is considered a promising design because it can solve the problem of high interfacial resistance of conventional solid‐state cathodes. However, solid discharge products cannot be efficiently decomposed in an integrated solid‐state cathode, resulting in batteries that are unable to operate for long periods of time. Herein, an integrated solid‐state cathode (Gel‐Tempo cathode) of sodium–air batteries (SABs) capable of promoting efficient decomposition of discharge product Na2O2 is designed. The Gel‐Tempo cathode is synthesized by cationic–π interaction of redox mediator 2,2,6,6‐tetramethyl‐1‐piperidinyloxy (Tempo) and ionic liquid with carbon nanotubes. The Gel‐Tempo cathode serves multiple functions as a redox mediator, flame retardancy, and high stability to air. In quasi‐solid‐state SABs, the Gel‐Tempo cathode reduces overpotential to 1.15 V and improves coulomb efficiency to 84.5% (at a limited discharge capacity of 3000 mAh g−1) compared to gel cathodes. Experiments and density functional theory calculations indicate that Tempo significantly reduces the Gibbs free energy in the decomposition reaction of Na2O2, and high Tempo content is more conducive to enhancing the decomposition kinetics of Na2O2 and hence resulting in an ultra‐long cycle life (1746 h). This work is crucial to promote practical applications of SABs, providing guidelines for functionalization design of integrated solid‐state cathodes for metal–air batteries.

Stability of NaO2 and LiO2 discharge products in metal-air batteries: density functional theory study

Rechargeable metal-air batteries are considered the next generation energy storage devices with the highest energy density of ~200 Wh/kg (which is much higher than the Li-ion batteries with ~150 Wh/kg). However, their practical applications are widely affected by the formation of unstable discharge products (like Na/LiO2, Na/Li2O, and Na/LiO) which react with electrolyte or the porous electrode material leading to either fire or explosion. Here, we explore the stability of the bulk pyrite and marcasite lithium/sodium superoxide (Li/NaO2) discharge products produced in Li and Na-air batteries using density functional theory calculations. The calculated lattice and heats of formations are consistent with available reported data. The electronic properties of show the Pnmm LiO2 as the most stable structure with the least density of states at the Fermi. The vibrational properties also show no imaginary vibrations in all directions for Pnmm LiO2. This finding can help direct and give an insight into the stability of major discharge products and give research direction towards controlling the formation of desired M-O discharge products in the batteries.

A comprehensive review of cathode materials for Na–air batteries

In recent years, rechargeable sodium–air batteries have attracted extensive attention and developed rapidly for electrochemical energy storage applications due to low costs, abundance of precursor resources, and high energy density.

DFT Studies of Catalytic Activity of Rutile Typed Metal Oxide (110) Surface in Sodium-Air Batteries

Metal-air batteries, such as Li-air, have been extensively studied owing to their high theoretical energy density, which is up to three times that of the conventional to Li-ion batteries and interest in Na-air is now emerging [1,2, 3]. The current study is providing a better understanding of the catalytic activity of rutile typed MO2 (MnO2, TiO2 and VO2) for the oxygen reduction and oxygen evolution reactions in Na-air batteries, using density functional methods. When oxygen is adsorbed at the Na/MO2 (110) surface different clusters, such as superoxide, peroxo on Na/M, and dissociated configurations are formed. Our current study has demonstrated that MnO2, as a catalyst, promotes nucleation and growth of both Na2O and Na2O2. On the contrary, other metal oxides such as TiO2 and VO2 do not depict this catalytic effect towards the formation of discharge products in Na-O2 batteries. Furthermore, it can be deduced from our calculated electronic properties, in the form of an intercept of the density of states (DOS) by the Fermi level, that Mn catalyzed configurations are more stable than those based on Ti and V. It can therefore be surmised that the MnO2 catalyst supports the formation of NaO2 which is the most stable discharge product in Na-air batteries. Furthermore, the surface NaO2 appears to have bond lengths comparable to those of the bulk and monomer NaO2.

A Reachable Sodium-Oxygen Battery Based on Sodium Superoxide Chemistry

Sodium-oxygen (Na-O2) batteries offer a great potential to provide high energy density storage systems needed for small-sized and inexpensive electric vehicles owing to the abundance of sodium compared with lithium. Yet, their development is hindered by the low cycle life and poor energy efficiencies due to (i) the formation of singlet oxygen, resulting in parasitic reactions with the air cathode and the organic electrolyte, (ii) the formation of unstable SEI layers and dendrites associated with the metallic sodium anode, and (iii) lack of an active, stable cathode catalyst to reduce the overpotentials and improve the cycle stability.Here, we have developed a Na-O2 battery cell composed of a highly active cathode catalyst that works well in synergy with an ether-based ionic-liquid electrolyte with specific redox mediators to act as co-catalysts to reversibly form and decompose sodium superoxide (NaO2) via surface-mediated pathway at a low polarization gap of about 40 mV at a capacity of 1000 mAh/g. Different electrochemical and physicochemical characterization techniques, i.e., Raman spectroscopy, XRD, XPS, DEMS, SEM, and TEM were used to understand the cell chemistry. Moreover, a chemically synthesized Na anode protection layer implemented in this battery cell enabled a long cycle life of 900 with all-time energy efficiencies more than 80%, exceeding state-of-art Na-O2 and Na-air batteries. The outcome of our study reveals the significance of the proper cell components design in Na-O2 battery technologies as a promising venue in energy conversion and storage systems.

Unravelling the Catalytic Activity of MnO2, TiO2, and VO2 (110) Surfaces by Oxygen Coadsorption on Sodium-Adsorbed MO2 {M = Mn, Ti, V}.

Metal-air batteries have attracted extensive research interest owing to their high theoretical energy density. However, most of the previous studies have been limited by applying pure oxygen in the cathode, without taking into consideration the effect of the catalyst, which plays a significant role in the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Adsorption of oxygen on (110) Na-MO2 is investigated, using density functional theory (DFT) calculations, which is important in the discharging and charging of Na-air batteries. Adsorption of oxygen on Na/MO2 was investigated, and it was observed that the catalysts encourage the formation of the discharge product reported in the literature, i.e., NaO2. The surface NaO2 appears to have bond lengths comparable to those reported for monomer NaO2.

Cobalt tetraphosphate as an efficient bifunctional electrocatalyst for hybrid sodium-air batteries

Economic and efficient bifunctional electrocatalysts are pivotal in realization of rechargeable (hybrid) metal-air batteries. It is ideal to employ noble-metal free bifunctional electrocatalysts that are not selective towards oxygen evolution and reduction (OER and ORR) activities. This work unveils cobalt-based tetraphosphate K2Co(PO3)4 as an economic bifunctional electrocatalyst acting as cathode for rechargeable hybrid sodium-air batteries. Autocombustion route led to the development of homogeneous, carbon-coated, spherical K2Co(PO3)4 nanoparticles enabling active site exposure to incoming guest molecules (O2, OH-). This monoclinic compound exhibited superior oxygen evolution activity with low overpotential (ca. 0.32 V) surpassing the commercial RuO2 catalyst. Tetraphosphate K2Co(PO3)4 was successfully implemented in hybrid Na-air batteries delivering reversible cycling with roundtrip efficiency over 70%. DFT study revealed this catalytic activity stem from the most active and stable surface (001) and half-metallic nature of Co in K2Co(PO3)4. Cobalt tetraphosphates can be harnessed to design low cost electrocatalysts for hybrid sodium-air batteries.

Nanoporous Gold for Energy Applications.

Research activities using nanoporous gold (NPG) were reviewed in the field of energy applications in three categories: fuel cells, supercapacitors, and batteries. First, applications to fuel cells are reviewed with the subsections of proof-of-concept studies, studies on fuel oxidations at anode, and studies on oxygen reduction reactions at cathode. Second, applications to supercapacitors are reviewed from research activities on active materials/NPG composites to demonstrations of all-solid-state flexible supercapacitors using NPG electrodes. Third, research activities using NPG for battery applications are reviewed, mainly about fundamental studies on Li-air and Na-air batteries and some model studies on improving Li ion battery anodes. Although NPG based studies are the main subject of this review, some of meaningful studies using nanoporous metals are also discussed where relevant. Finally, summary and future outlook are given based on the survey on the research activities.

Prevention of Na Corrosion and Dendrite Growth for Long-Life Flexible Na-Air Batteries.

Rechargeable Na–air batteries (NABs) based on abundant Na resources are generating great interest due to their high energy density and low cost. However, Na anode corrosion in ambient air and the growth of abnormal dendrites lead to insufficient cycle performance and safety hazards. Effectively protecting the Na anode from corrosion and inducing the uniform Na plating and stripping are therefore of vital importance for practical application. We herein report a NAB with in situ formed gel electrolyte and Na anode with trace residual Li. The gel electrolyte is obtained within cells through cross-linking Li ethylenediamine at the anode surface with tetraethylene glycol dimethyl ether (G4) from the liquid electrolyte. The gel can effectively prevent H2O and O2 crossover, thus delaying Na anode corrosion and electrolyte decomposition. Na dendrite growth was suppressed by the electrostatic shield effect of Li+ from the modified Li layer. Benefiting from these improvements, the NAB achieves a robust cycle performance over 2000 h in opened ambient air, which is superior to previous results. Gelation of the electrolyte prevents liquid leakage during battery bending, facilitating greater cell flexibility, which could lead to the development of NABs suitable for wearable electronic devices in ambient air.

Preparation of Electrocatalysts and Comparison of Electrode Interface Reaction for Hybrid Type Na-air Battery

Preparation of Electrocatalysts and Comparison of Electrode Interface Reaction for Hybrid Type Na-air Battery

Realization of good performance of Na-air Battery in real Air Condition

Hybrid sodium-air battery possess higher theoretical open circuit voltage and theoretical specific capacity of 2600 Wh·kg−1, as well as lower over potential compared to nonaqueous sodium-air batteries.

The effect of CO2 contamination in rechargeable non-aqueous sodium-air batteries.

Metal-air batteries have higher theoretical specific energies than existing rechargeable batteries including Li-ion batteries. Among metal-air batteries, the Na-O2 battery has gained much attention due to its low discharge/charge overpotentials (∼100 mV) at relatively high current densities (0.2 mA/cm2), high electrical energy efficiency (90%), high theoretical energy density, and low cost. However, there is no information reported regarding the effect of CO2 contamination in non-aqueous Na-air batteries. Density functional theory has, here, been applied to study the effect of low concentrations of CO2 contamination on NaO2 and Na2O2 growth/depletion reaction pathways and overpotentials. This was done on step surfaces of discharge products in non-aqueous Na-air batteries. Adsorption energies of CO2 at various nucleation sites for both step surfaces were determined, and results revealed that CO2 preferentially binds at the step valley sites of (001) NaO2 and 11¯00 Na2O2 surfaces with binding energies of -0.65 eV and -2.67 eV, respectively. CO2 blocks the step nucleation site and influences the reaction pathways and overpotentials due to carbonate formation. The discharge electrochemical overpotential increases remarkably from 0.14 V to 0.30 V and from 0.69 V to 1.26 V for NaO2 and Na2O2 surfaces, respectively. CO2 contamination is thus drastically impeding the growth/depletion mechanism pathways and increases the overpotentials of the surface reaction mechanism, hampering the performance of the battery. Avoiding CO2 contamination from intake of gas and electrolyte decomposition is thus critical in development of Na-air batteries.

Can Hybrid Na-Air Batteries Outperform Nonaqueous Na-O2 Batteries?

In recent years, there has been an upsurge in the study of novel and alternative energy storage devices beyond lithium‐based systems due to the exponential increase in price of lithium. Sodium (Na) metal‐based batteries can be a possible alternative to lithium‐based batteries due to the similar electrochemical voltage of Na and Li together with the thousand times higher natural abundance of Na compared to Li. Though two different kinds of Na–O2 batteries have been studied specifically based on electrolytes until now, very recently, a hybrid Na–air cell has shown distinctive advantage over nonaqueous cell systems. Hybrid Na–air batteries provide a fundamental advantage due to the formation of highly soluble discharge product (sodium hydroxide) which leads to low overpotentials for charge and discharge processes, high electrical energy efficiency, and good cyclic stability. Herein, the current status and challenges associated with hybrid Na–air batteries are reported. Also, a brief description of nonaqueous Na–O2 batteries and its close competition with hybrid Na–air batteries are provided.

Immobilizing single atom catalytic sites onto highly reduced carbon hosts: Fe–N4/CNT as a durable oxygen reduction catalyst for Na–air batteries

Immobilizing metal ions on a carbon support usually involves severe aggregation (sintering) and loose attachment of metal ions owing to a weak metal–support interaction.

Highly dispersed Co nanoparticles decorated on a N-doped defective carbon nano-framework for a hybrid Na-air battery.

Efficient and low-cost bifunctional electrocatalysts for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) are of vital importance in energy conversion. Herein, an excellent highly dispersed Co nanoparticle decorated N-doped defective carbon nano-framework (Co-N-C) derived from a ZnCo bimetal organic framework (bi-MOF) is reported. A high specific surface area originating from zinc evaporation facilitates the adsorption and desorption of oxygen, which promotes the accessibility of catalytic sites. The abundant Co-N-C species act as strong bridging bonds between Co nanoparticles and carbon materials which facilitate interfacial electron transfer. Co-N-C-0.5 (0.5 represents the molar ratio of Zn in the initial ZIF-67) exhibits a low overpotential gap of 0.94 V due to the number of active sites (e.g. N-doped defective carbon and the CoNx/Co composite) and fast interfacial electron transfer. In addition, a hybrid Na-air battery with the Co-N-C-0.5 material displays a low voltage gap of 0.31 V and a high round-trip efficiency of 90.0% at a current density of 0.1 mA cm-2. More importantly, the hybrid Na-air battery shows fantastic cyclability for charging and discharging due to its stable structure. Our results confirm Co-N-C materials derived from a bi-MOF as alternatives to high-cost Pt/C catalysts for ORR and OER activities in metal-air batteries.

Toward materials-by-design: achieving functional materials with physical and chemical effects

Advances in renewable and sustainable energy technologies critically depend on our ability to rationally design and process target materials with optimized performances. Advanced material design and discovery are ideally involved in material prediction, synthesis and characterization. Control of material crystallization enables the rational design and discovery of novel functional inorganic materials in multi-scale. Material processing can be adjusted by various physical fields and chemical effects at different energy states. Material microstructure, architecture and functionality can thus be modified by multiple design methodologies. In this review, we show typical examples using physical and chemical methods to shape inorganic functional materials and evaluate their specific applications in Na-air batteries, Li-ion batteries and supercapacitors. Furthermore, this review also provides insight into the understanding of synthesis-structure relationship of inorganic functional materials.