Alkaline Ni-Zn Rechargeable Batteries for Sustainable Energy Storage: Battery Components, Deterioration Mechanisms, and Impact of Additives.

The demand for long-term, sustainable, and low-cost battery energy storage systems with high power delivery capabilities for stationary grid-scale energy storage, as well as the necessity for safe lithium-ion battery alternatives, has renewed interest in aqueous zinc-based rechargeable batteries. The alkaline Ni-Zn rechargeable battery chemistry was identified as a promising technology for sustainable energy storage applications, albeit a considerable investment in academic research, it still fails to deliver the requisite performance. It is hampered by a relatively short-term electrode degradation, resulting in a decreased cycle life. Dendrite formation, parasitic hydrogen evolution, corrosion, passivation, and dynamic morphological growth are all challenging and interrelated possible degradation processes. This review elaborates on the components of Ni-Zn batteries and their deterioration mechanisms, focusing on the influence of electrolyte additives as a cost-effective, simple, yet versatile approach for regulating these phenomena and extending the battery cycle life. Even though a great deal of effort has been dedicated to this subject, the challenges remain. This highlights that a breakthrough is to be expected, but it will necessitate not only an experimental approach, but also a theoretical and computational one, including artificial intelligence (AI) and machine learning (ML).

Galvanostatic Fast Charging of Alkali-Ion Battery Materials at the Single-Particle Level: A Map-Driven Diagnosis.

In this work, we develop a new tool to provide a diagnostic map for alkali-ion intercalation materials under galvanostatic conditions. These representations, stated in the form of capacity level diagrams, are built from hundreds of numerical simulations representing different experimental conditions, summarized in two dimensionless parameters: a kinetic parameter denominated Ξ and a finite diffusion parameter l. To lay the theoretical and methodological foundations, a general model is used here. This model can be adapted to the thermodynamic and kinetic framework of specific systems. We provide two representative examples.

AZ31 Magnesium Alloy Foils as Thin Anodes for Rechargeable Magnesium Batteries.

In recent decades, rechargeable Mg batteries (RMBs) technologies have attracted much attention because the use of thin Mg foil anodes may enable development of high-energy-density batteries. One of the most critical challenges for RMBs is finding suitable electrolyte solutions that enable efficient and reversible Mg cells operation. Most RMB studies concentrate on the development of novel electrolyte systems, while only few studies have focused on the practical feasibility of using pure metallic Mg as the anode material. Pure Mg metal anodes have been demonstrated to be useful in studying the fundamentals of nonaqueous Mg electrochemistry. However, pure Mg metal may not be suitable for mass production of ultrathin foils (<100 microns) due to its limited ductility. The metals industry overcomes this problem by using ductile Mg alloys. Herein, the feasibility of processing ultrathin Mg anodes in electrochemical cells was demonstrated by using AZ31 Mg alloys (3 % Al; 1 % Zn). Thin-film Mg AZ31 anodes presented reversible Mg dissolution and deposition behavior in complex ethereal Mg electrolytes solutions that was comparable to that of pure Mg foils. Moreover, it was demonstrated that secondary Mg battery prototypes comprising ultrathin AZ31 Mg alloy anodes (≈25 µm thick) and Mgx Mo6 S8 Chevrel-phase cathodes exhibited cycling performance equal to that of similar cells containing thicker pure Mg foil anodes. The possibility of using ultrathin processable Mg metal anodes is an important step in the realization of rechargeable Mg batteries.

Enhanced Electrochemical Performance of Supercapacitors via Atomic Layer Deposition of ZnO on the Activated Carbon Electrode Material.

Fabricating electrical double-layer capacitors (EDLCs) with high energy density for various applications has been of great interest in recent years. However, activated carbon (AC) electrodes are restricted to a lower operating voltage because they suffer from instability above a threshold potential window. Thus, they are limited in their energy storage. The deposition of inorganic compounds' atomic layer deposition (ALD) aiming to enhance cycling performance of supercapacitors and battery electrodes can be applied to the AC electrode materials. Here, we report on the investigation of zinc oxide (ZnO) coating strategy in terms of different pulse times of precursors, ALD cycles, and deposition temperatures to ensure high electrical conductivity and capacitance retention without blocking the micropores of the AC electrode. Crystalline ZnO phase with its optimal forming condition is obtained preferably using a longer precursor pulse time. Supercapacitors comprising AC electrodes coated with 20 cycles of ALD ZnO at 70 °C and operated in TEABF4/acetonitrile organic electrolyte show a specific capacitance of 23.13 F g-1 at 5 mA cm-2 and enhanced capacitance retention at 3.2 V, which well exceeds the normal working voltage of a commercial EDLC product (2.7 V). This work delivers an additional feasible approach of using ZnO ALD modification of AC materials, enhancing and promoting stable EDLC cells under high working voltages.

Atomic Layer Deposition (ALD) of Alumina over Activated Carbon Electrodes Enabling a Stable 4†V Supercapacitor Operation.

Designing high voltage (>3 V) and stable electrochemical supercapacitors with low self-discharge is desirable for the applications in modern electronic devices. This work demonstrates a 4 V symmetric supercapacitor with stabilized cycling performance through atomic layer deposition (ALD) of alumina (Al2 O3 ) on the surface of activated carbon (AC). The 20-cycle ALD Al2 O3 coated AC delivers 84 % capacitance retention after 1000 charge/discharge cycles under 4 V, contrary to the bare AC cells having only 48 % retention. The extended cycling life is associated with the thickened Stern layer and suppressed oxygen functional group. The self-discharge data also show that the Al2 O3 coating enables AC cells to maintain 53 % of charge retention after 12 h, which is more than twice higher than that of bare AC cells under the same test protocol of 4 V charging. The curve fitting analysis reveals that ALD coating induced slow self-discharge dominated by ion diffusion mechanism, thus enhancing the AC surface energy.

Bio-Derived Carbon with Tailored Hierarchical Pore Structures and Ultra-High Specific Surface Area for Superior and Advanced Supercapacitors.

We report here on a hollow-fiber hierarchical porous carbon exhibiting an ultra-high specific surface area, synthesized by a facile method of carbonization and activation, using the Metaplexis Japonica (MJ) shell. The Metaplexis Japonica-based activated carbon demonstrated a very high specific surface area of 3635 m2 g-1. Correspondingly, the derived carbonaceous material delivers an ultra-high capacitance and superb cycle life in an alkaline electrolyte. The pore-ion size compatibility is optimized using tailored hierarchical porous carbon and different ion sized organic electrolytes. In ionic liquids nonaqueous based electrolytes we tailored the MJ carbon pore structure to the electrolyte ion size. The corresponding supercapacitor shows a superior rate performance and low impedance, and the device records specific energy and specific power densities as high as 76 Wh kg-1 and 6521 W kg-1, as well as a pronounced cycling durability in the ionic liquid electrolytes. Overall, we suggest a protocol for promising carbonaceous electrode materials enabling superior supercapacitors performance.

Direct Pre-lithiation of Electropolymerized Carbon Nanotubes for Enhanced Cycling Performance of Flexible Li-Ion Micro-Batteries.

Carbon nanotubes (CNT) are used as anodes for flexible Li-ion micro-batteries. However, one of the major challenges in the growth of flexible micro-batteries with CNT as the anode is their immense capacity loss and a very low initial coulombic efficiency. In this study, we report the use of a facile direct pre-lithiation to suppress high irreversible capacity of the CNT electrodes in the first cycles. Pre-lithiated polymer-coated CNT anodes displayed good rate capabilities, studied up to 30 C and delivered high capacities of 850 mAh g-1 (313 µAh cm-2) at 1 C rate over 50 charge-discharge cycles.

Layered Boron-Nitrogen-Carbon-Oxygen Materials with Tunable Composition as Lithium-Ion Battery Anodes.

The insertion of heteroatoms with different electronegativity into carbon materials can tune their chemical, electronic, and optical properties. However, in traditional solid-state synthesis, it is challenging to control the reactivity of monomers, and therefore, the amount and position of heteroatoms in the final materials. Herein, a simple, scalable, and general molten-state route to synthesize boron-nitrogen-carbon-oxygen (BNCO) materials with tunable boron-nitrogen-carbon composition, as well as electronic and optical properties, is reported. The new synthetic approach consists of polycyclic aromatic hydrocarbons (PAHs) and ammonia-borane as reactants that form a clear liquid-state stage spanning a wide temperature range, before the solid-state reaction. The molten-state stage enhances the control over the synthetic intermediates and final materials, owing to improved monomer miscibility and reactivity. The BNCO composition and optical properties are tuned by the PAH selection and final reaction temperature. The advantages of this method are demonstrated herein through the tunable optical properties, excellent stability to oxidization, facile deposition on substrates, and good activity as an anode material in lithium-ion batteries.

Low voltage electric potential as a driving force to hinder biofouling in self-supporting carbon nanotube membranes.

This study aimed at evaluating the contribution of low voltage electric field, both alternating (AC) and direct (DC) currents, on the prevention of bacterial attachment and cell inactivation to highly electrically conductive self-supporting carbon nanotubes (CNT) membranes at conditions which encourage biofilm formation. A mutant strain of Pseudomonas putida S12 was used a model bacterium and either capacitive or resistive electrical circuits and two flow regimes, flow-through and cross-flow filtration, were studied. Major emphasis was placed on AC due to its ability of repulsing and inactivating bacteria. AC voltage at 1.5 V, 1 kHz frequency and wave pulse above offset (+0.45) with 100Ω external resistance on the ground side prevented almost completely attachment of bacteria (>98.5%) with concomitant high inactivation (95.3 ± 2.5%) in flow-through regime. AC resulted more effective than DC, both in terms of biofouling reduction compared to cathodic DC and in terms of cell inactivation compared to anodic DC. Although similar trends were observed, a net reduced extent of prevention of bacterial attachment and inactivation was observed in filtration as compared to flow-through regime, which is mainly attributed to the permeate drag force, also supported by theoretical calculations in DC in capacitive mode. Electrochemical impedance spectroscopy analysis suggests a pure resistor behavior in resistance mode compared to involvement of redox reactions in capacitance mode, as source for bacteria detachment and inactivation. Although further optimization is required, electrically polarized CNT membranes offer a viable antibiofouling strategy to hinder biofouling and simplify membrane care during filtration.

The Role of Air-Electrode Structure on the Incorporation of Immiscible PFCs in Nonaqueous Li-O2 Battery.

Perfluorocarbons (PFCs) are considered advantageous additives to nonaqueous Li-O2 battery due to their superior oxygen solubility and diffusivity compared to common battery electrolytes. Up to now, the main focus was concentrated on PFCs-electrolyte investigation; however, no special attention was granted to the role of carbon structure in the PFCs-Li-O2 system. In our current research, immiscible PFCs, rather than miscible fluorinated ethers, were added to activated carbon class air electrode due to their higher susceptibility toward O2•- attack and to their ability to shift the reaction from two-phase to an artificial three-phase reaction zone. The results showed superior battery performance upon PFCs addition at lower current density (0.05 mA cm-2) but unexpectedly failed to do so at higher current density (0.1 and 0.2 mA cm-2), where oxygen transport limitation is best illustrated. The last was a direct result of liquid-liquid displacement phenomenon occurring when the two immiscible liquids were introduced into the porous carbon medium. The investigation and role of carbon structure on the mechanism upon PFCs addition to Li-O2 system are suggested based on electrochemical characterization, wettability behavior studies, and the physical adsorption technique. Finally, we suggest an optimum air-electrode structure enabling the incorporation of immiscible PFCs in a nonaqueous Li-O2 battery.

Challenges and Prospect of Non-aqueous Non-alkali (NANA) Metal-Air Batteries.

Non-aqueous non-alkali (NANA) metal-air battery technologies promise to provide electrochemical energy storage with the highest specific energy density. Metal-air battery technology is particularly advantageous being implemented in long-range electric vehicles. Up to now, almost all the efforts in the field are focused on Li-air cells, but other NANA metal-air battery technologies emerge. The major concern, which the research community should be dealing with, is the limited and rather poor rechargeability of these systems. The challenges we are covering in this review are related to the initial limited discharge capacities and cell performances. By comprehensively reviewing the studies conducted so far, we show that the implementation of advanced materials is a promising approach to increase metal-air performance and, particularly, metal surface activation as a prime achievement leading to respectful discharge currents. In this review, we address the most critical areas that need careful research attention in order to achieve progress in the understanding of the physical and electrochemical processes in non-aqueous electrolytes applied in beyond lithium and zinc air generation of metal-air battery systems.

Improvement of Aluminum-Air Battery Performances by the Application of Flax Straw Extract.

The effect of a flax straw extract on Al corrosion inhibition in a strong alkaline solution was studied by using electrochemical measurements, weight-loss analysis, SEM, and FTIR spectroscopy. Flax straw extract added (3 vol %) to the 5 m KOH solution to act as a mixed-type Al corrosion inhibitor. The electrochemistry of Al in the presence of a flax straw extract in the alkaline solution, the effect of the extract on the Al morphology and surface films formed, and the corrosion inhibition mechanism are discussed. Finally, the Al-air battery discharge capacity recorded from a cell that used the flax straw extract in the alkaline electrolyte is substantially higher than that with only a pure alkaline electrolyte. This improved sustainability of the Al anode is attributed to Al corrosion inhibition and, consequently, to hydrogen evolution suppression.

PFC and Triglyme for Li-Air Batteries: A Molecular Dynamics Study.

In this work, we present an all-atom molecular dynamics (MD) study of triglyme and perfluorinated carbons (PFCs) using classical atomistic force fields. Triglyme is a typical solvent used in nonaqueous Li-air battery cells. PFCs were recently reported to increase oxygen availability in such cells. We show that O2 diffusion in two specific PFC molecules (C6F14 and C8F18) is significantly faster than in triglyme. Furthermore, by starting with two very different initial configurations for our MD simulation, we demonstrate that C8F18 and triglyme do not mix. The mutual solubility of these molecules is evaluated both theoretically and experimentally, and a qualitative agreement is found. Finally, we show that the solubility of O2 in C8F18 is considerably higher than in triglyme. The significance of these results to Li-air batteries is discussed.

Influence of solution volume on the dissolution rate of silicon dioxide in hydrofluoric acid.

Experimental data and modeling of the dissolution of various Si/SiO2 thermal coatings in different volumes of hydrofluoric acid (HF) are reported. The rates of SiO2 -film dissolution, measured by means of various electrochemical techniques, and alteration in HF activity depend on the thickness of the film coating. Despite the small volumes (0.6-1.2 mL) of the HF solution, an effect of SiO2 -coating thickness on the dissolution rate was detected. To explain alterations detected in HF activity after SiO2 dissolution, spectroscopic analyses (NMR and FTIR) of the chemical composition of the solutions were conducted. This is associated with a modification in the chemical composition of the HF solution, which results in either the formation of an oxidized species in solution or the precipitation of dissolution products. HF2 (-) accumulation in the HF solution, owing to SiO2 dissolution was identified as the source of the chemical alteration.

Liquid-free lithium-oxygen batteries.

Non-aqueous lithium-oxygen batteries are considered as most advanced power sources, albeit they are facing numerous challenges concerning almost each cell component. Herein, we diverge from the conventional and traditional liquid-based non-aqueous Li-O2 batteries to a Li-O2 system based on a solid polymer electrolyte (SPE-) and operated at a temperature higher than the melting point of the polymer electrolyte, where useful and most applicable conductivity values are easily achieved. The proposed SPE-based Li-O2 cell is compared to Li-O2 cells based on ethylene glycol dimethyl ether (glyme) through potentiodynamic and galvanostatic studies, showing a higher cell discharge voltage by 80 mV and most significantly, a charge voltage lower by 400 mV. The solid-state battery demonstrated a comparable discharge-specific capacity to glyme-based Li-O2 cells when discharged at the same current density. The results shown here demonstrate that the safer PEO-based Li-O2 battery is highly advantageous and can potentially replace the contingent of liquid-based cells upon further investigation.

A critical review on lithium-air battery electrolytes.

Metal-air batteries, utilizing the reduction of ambient oxygen, have the highest energy density because most of the cell volume is occupied by the anode while the cathode active material is not stored in the battery. Lithium metal is a tempting anode material for any battery because of its outstanding specific capacity (3842 mA h g(-1) for Li vs. 815 mA h g(-1) for Zn). Combining the high energy density of Li with ambient oxygen seems to be a promising option. Specifically, in all classes of electrolytes, the transformation from Li-O2 to Li-air is still a major challenge as the presence of moisture and CO2 reduces significantly the cell performance due to their strong reaction with Li metal. Thus, the quest for electrolyte systems capable of providing a solution to the imposed challenges due to the use of metallic Li, exposure to the environment and handling the formation of reactive discharged product is still on. This extended Review provides an expanded insight into electrolytes being suggested and researched and also a future vision on challenges and their possible solutions.

Reference electrode assembly and its use in the study of fluorohydrogenate ionic liquid silicon electrochemistry.

Silicon electrochemistry in fluorohydrogenate ionic liquids is partly hampered owing to the incapability of producing an accurate and reproducible potential measurement due to a lack of appropriate reference electrodes. This research work describes a simple assembly of a stable external reference electrode enabling accurate studies of silicon electrochemistry in fluorohydrogenate ionic liquids. The electrode configuration is based on the ferrocene/ferrocenium (Fc|Fc(+)) couple dissolved in the EMIm(HF)(2.3)F (1-ethyl-3-methyl-imidazolium fluorohydrogenate)/Carbopol 941 gel. A stable potential of 2.5 wt% Carbopol-based electrode was measured versus a calomel reference electrode at 250 ± 3 mV. By utilizing the constructed electrode, an intensive electrochemical investigation on n-type silicon in EMIm(HF)(2.3)F was conducted. Flat-band and open circuit potentials were measured, along with Si-air half- and full-cell electrochemical measurements. A suggested mechanism for the n-type Si dissolution process in the EMIm(HF)(2.3)F electrolyte, without illumination, is discussed as well.

New insight into the discharge mechanism of silicon-air batteries using electrochemical impedance spectroscopy.

The mechanism of discharge termination in silicon-air batteries, employing a silicon wafer anode, a room-temperature fluorohydrogenate ionic liquid electrolyte and an air cathode membrane, is investigated using a wide range of tools. EIS studies indicate that the interfacial impedance between the electrolyte and the silicon wafer increases upon continuous discharge. In addition, it is shown that the impedance of the air cathode-electrolyte interface is several orders of magnitude lower than that of the anode. Equivalent circuit fitting parameters indicate the difference in the anode-electrolyte interface characteristics for different types of silicon wafers. Evolution of porous silicon surfaces at the anode and their properties, by means of estimated circuit parameters, is also presented. Moreover, it is found that the silicon anode potential has the highest negative impact on the battery discharge voltage, while the air cathode potential is actually stable and invariable along the whole discharge period. The discharge capacity of the battery can be increased significantly by mechanically replacing the silicon anode.

Limitation of discharge capacity and mechanisms of air-electrode deactivation in silicon-air batteries.

The electrocatalytical process at the air cathode in novel silicon-air batteries using the room-temperature ionic liquid hydrophilic 1-ethyl-3-methylimidazolium oligofluorohydrogenate [EMI⋅2.3 HF⋅F] as electrolyte and highly doped silicon wafers as anodes is investigated by electrochemical means, X-ray photoelectron spectroscopy (XPS), and electron paramagnetic resonance (EPR) spectroscopy. The results obtained by XPS and EPR provide a model to describe the limited discharge capacity by means of a mechanism of air-electrode deactivation. In that respect, upon discharge the silicon-air battery's cathode is not only blocked by silicon oxide reduction products, but also experiences a major modification in the MnO2 catalyst nature. The proposed modification of the MnO2 catalyst by means of a MnF2 surface layer greatly impacts the Si-air performance and describes a mechanism relevant for other metal-air batteries, such as the lithium-air. Moreover, the ability for this deactivation layer to form is greatly impacted by water in the electrolyte.