Fast discharge process of layered cobalt oxides due to high Na⁺ diffusion

Sodium layered oxide cathodes: properties, practicality and prospects

Rechargeable sodium-ion batteries (SIBs) have emerged as an advanced electrochemical energy storage technology with potential to alleviate the dependence on lithium resources. Similar to Li-ion batteries, the cathode materials play a decisive role in the cost and energy output of SIBs. Among various cathode materials, Na layered transition-metal (TM) oxides have become an appealing choice owing to their facile synthesis, high Na storage capacity/voltage that are suitable for use in high-energy SIBs, and high adaptivity to the large-scale manufacture of Li layered oxide analogues. However, going from the lab to the market, the practical use of Na layered oxide cathodes is limited by the ambiguous understanding of the fundamental structure-performance correlation of cathode materials and lack of customized material design strategies to meet the diverse demands in practical storage applications. In this review, we attempt to clarify the fundamental misunderstandings by elaborating the correlations between the electron configuration of the critical capacity-contributing elements (e.g., TM cations and oxygen anion) in oxides and their influence on the Na (de)intercalation (electro)chemistry and storage properties of the cathode. Subsequently, we discuss the issues that hinder the practical use of layered oxide cathodes, their origins and the corresponding strategies to address their issues and accelerate the target-oriented research and development of cathode materials. Finally, we discuss several new Na layered cathode materials that show prospects for next-generation SIBs, including layered oxides with anion redox and high entropy and highlight the use of layered oxides as cathodes for solid-state SIBs with higher energy and safety. In summary, we aim to offer insights into the rational design of high-performance Na layered oxide cathode materials towards the practical realization of sustainable electrochemical energy storage at a low cost.

Uncovering the predictive pathways of lithium and sodium interchange in layered oxides

Ion exchange is a powerful method to access metastable materials with advanced functionalities for energy storage applications. However, high concentrations and unfavourably large excesses of lithium are always used for synthesizing lithium cathodes from parent sodium material, and the reaction pathways remain elusive. Here, using layered oxides as model materials, we demonstrate that vacancy level and its corresponding lithium preference are critical in determining the accessible and inaccessible ion exchange pathways. Taking advantage of the strong lithium preference at the right vacancy level, we establish predictive compositional and structural evolution at extremely dilute and low excess lithium based on the phase equilibrium between Li0.94CoO2 and Na0.48CoO2. Such phase separation behaviour is general in both surface reaction-limited and diffusion-limited exchange conditions and is accomplished with the charge redistribution on transition metals. Guided by this understanding, we demonstrate the synthesis of NayCoO2 from the parent LixCoO2 and the synthesis of Li0.94CoO2 from NayCoO2 at 1-1,000 Li/Na (molar ratio) with an electrochemical assisted ion exchange method by mitigating the kinetic barriers. Our study opens new opportunities for ion exchange in predictive synthesis and separation applications.

Chloride electrode composed of ubiquitous elements for high-energy-density all-solid-state sodium-ion batteries

Inexpensive and safe energy-storage batteries with high energy densities are in high demand (e.g., for electric vehicles and grid-level renewable energy storage). This study focused on using NaFeCl4, comprising ubiquitous elements, as an electrode material for all-solid-state sodium-ion batteries. Monoclinic NaFeCl4, expected to be the most resource-attractive Fe redox material, is also thermodynamically stable. The Fe2+/3+ redox reaction of the monoclinic NaFeCl4 electrode has a higher potential (3.45 V vs. Na/Na+) than conventional oxide electrodes (e.g., Fe2O3 with 1.5 V vs. Na/Na+) because of the noble properties of chlorine. Additionally, NaFeCl4 exhibits unusually high deformability (99% of the relative density of the pellet) upon uniaxial pressing (382 MPa) at 298 K. NaFeCl4 operates at 333 K in an electrode system containing no electrolyte, thereby realizing next-generation all-solid-state batteries with high safety. A high energy density per positive electrode of 281 Wh kg-1 was achieved using only a simple powder press.

Recent Advances in Sodium-Ion Batteries: Cathode Materials

Emerging energy storage systems have received significant attention along with the development of renewable energy, thereby creating a green energy platform for humans. Lithium-ion batteries (LIBs) are commonly used, such as in smartphones, tablets, earphones, and electric vehicles. However, lithium has certain limitations including safety, cost-effectiveness, and environmental issues. Sodium is believed to be an ideal replacement for lithium owing to its infinite abundance, safety, low cost, environmental friendliness, and energy storage behavior similar to that of lithium. Inhered in the achievement in the development of LIBs, sodium-ion batteries (SIBs) have rapidly evolved to be commercialized. Among the cathode, anode, and electrolyte, the cathode remains a significant challenge for achieving a stable, high-rate, and high-capacity device. In this review, recent advances in the development and optimization of cathode materials, including inorganic, organometallic, and organic materials, are discussed for SIBs. In addition, the challenges and strategies for enhancing the stability and performance of SIBs are highlighted.

Attachment of facile synthesized NaCo2O4 nanodots to SiO2 nanoflakes for sodium-rich boosted Pt-dominated ambient HCHO oxidation

Surface alkali metal ions are typically utilized as available promoters for ambient HCHO oxidation. In this study, NaCo₂O₄ nanodots with two different preferential crystallographic orientations are synthesized by facile attachment to SiO₂ nanoflakes with varying degrees of lattice defects. A unique Na-rich environment is established through interlayer Na⁺ diffusion based on the small size effect. The optimized catalyst Pt/HNaCo₂O₄/T₂ can deal with HCHO below 5 ppm in the static measurement system with a sustained release background and produces approximately 40 ppm of CO₂ in 2 h. Combining the experimental analyses with density functional theory (DFT) calculations, the possible catalytic enhancing mechanism is proposed from the support promotion perspective, and the positive synergistic effect of Na-rich, oxygen vacancies and optimized facets for Pt-dominant ambient HCHO oxidation via both kinetic and thermodynamic processes is confirmed.

Discharge State of Layered P2-Type Cathode Reveals Unsafe than Charge Condition in Thermal Runaway Event for Sodium-Ion Batteries

A sol-gel process followed by heat treatment derived a layered P2-type NaCoO₂ cathode, which depicted unit cell parameters values of a = 2.8389 Å, c = 10.9899 Å, and V = 76.71 ų in powder X-ray diffraction pattern. The synthesized cathode exhibited hexagonal, 2D platelets with an ∼300 nm thickness. During the anodic and cathodic sweeps, the cyclic voltammograms revealed multiple redox peaks with the same current densities, shapes, and peak positions, associated with the highly reversible phase transition mechanism of the layered P2-type NaCoO₂ cathode. The sodium cells yielded the capacities of 93/92 mAh g^-1 at 0.5 C and 87/87 mAh g^-1 at 1 C for the 50th charge-discharge cycles. The in situ multimode calorimetry (MMC) studies of sodium cells demonstrated a thermal explosion event, which occurred by sodium melting, short-circuit, electrode decomposition reaction, gas generation, exothermic reaction, released heat energy ,and cell gasket melting. Ultimately, the calculated released total heat energies of ∼550/740 J g^-1 for in situ MMC studies and ∼312/594 J g^-1 for ex situ DSC analyses (charge state at 4 V and discharge state at 2 V) show that the discharged state of sodiated layered P2-type NaCoO₂ cathode material is more unsafe than the charge state. Furthermore, the ex situ differential scanning calorimetry (DSC) spectrum of a discharge state at 2 V of layered P2-type NaCoO₂ revealed a decreased onset temperature (DOT) at 141 °C with two pronounced exothermic peaks at 197 and 266 °C with a released higher total heat energy of 594 J g^-1 than the charge state heat energy at 312 J g^-1, attributed to the higher charge onset temperature (COT) at 191 °C. Thus, the observed higher heat energy and decreased onset temperature for the discharge state at 2 V is associated with the higher Na⁺ ion in the discharge state of the layered P2-type Na_xCoO₂ cathode than that of the pristine cathode, showcasing that the layered P2-type NaCoO₂ cathode is unsafe at the discharged condition for sodium-ion batteries.

Electrodeposition of atmosphere-sensitive ternary sodium transition metal oxide films for sodium-based electrochemical energy storage

We introduce an intermediate-temperature (350 °C) dry molten sodium hydroxide-mediated binder-free electrodeposition process to grow the previously electrochemically inaccessible air- and moisture-sensitive layered sodium transition metal oxides, Na_xMO₂ (M = Co, Mn, Ni, Fe), in both thin and thick film form, compounds which are conventionally synthesized in powder form by solid-state reactions at temperatures ≥700 °C. As a key motivation for this work, several of these oxides are of interest as cathode materials for emerging sodium-ion-based electrochemical energy storage systems. Despite the low synthesis temperature and short reaction times, our electrodeposited oxides retain the key structural and electrochemical performance observed in high-temperature bulk synthesized materials. We demonstrate that tens of micrometers thick >75% dense Na_xCoO₂ and Na_xMnO₂ can be deposited in under 1 h. When used as cathodes for sodium-ion batteries, these materials exhibit near theoretical gravimetric capacities, chemical diffusion coefficients of Na⁺ ions (∼10^-12 cm²⋅s^-1), and high reversible areal capacities in the range ∼0.25 to 0.76 mA⋅h⋅cm^-2, values significantly higher than those reported for binder-free sodium cathodes deposited by other techniques. The method described here resolves longstanding intrinsic challenges associated with traditional aqueous solution-based electrodeposition of ceramic oxides and opens a general solution chemistry approach for electrochemical processing of hitherto unexplored air- and moisture-sensitive high valent multinary structures with extended frameworks.

Promises and Challenges of Next-Generation "Beyond Li-ion" Batteries for Electric Vehicles and Grid Decarbonization

The tremendous improvement in performance and cost of lithium-ion batteries (LIBs) have made them the technology of choice for electrical energy storage. While established battery chemistries and cell architectures for Li-ion batteries achieve good power and energy density, LIBs are unlikely to meet all the performance, cost, and scaling targets required for energy storage, in particular, in large-scale applications such as electrified transportation and grids. The demand to further reduce cost and/or increase energy density, as well as the growing concern related to natural resource needs for Li-ion have accelerated the investigation of so-called "beyond Li-ion" technologies. In this review, we will discuss the recent achievements, challenges, and opportunities of four important "beyond Li-ion" technologies: Na-ion batteries, K-ion batteries, all-solid-state batteries, and multivalent batteries. The fundamental science behind the challenges, and potential solutions toward the goals of a low-cost and/or high-energy-density future, are discussed in detail for each technology. While it is unlikely that any given new technology will fully replace Li-ion in the near future, "beyond Li-ion" technologies should be thought of as opportunities for energy storage to grow into mid/large-scale applications.

Enhancing Oxygen Vacancies by Introducing Na+ into OMS-2 Tunnels To Promote Catalytic Ozone Decomposition

A series of Na-OMS-2 catalysts was prepared by a facile solid-state reaction method. Their physiochemical properties were characterized, and the catalytic activity for ozone decomposition was evaluated. The results showed that the introduction of Na⁺ in the tunnel framework of OMS-2 facilitated lattice defect formation, which significantly enhanced oxygen vacancies, which are believed to be the active sites for ozone decomposition. Density functional theory calculations also showed that both the oxygen vacancy formation energy and ozone adsorption energy over Na-OMS-2 decreased because of Na⁺ introduction. Sodium ion introduction significantly improved the OMS-2 catalytic activity for ozone decomposition. The Na-OMS-2 catalyst with a Na/Mn molar ratio of 1/4 exhibited ozone conversion at 92.5% at 25 ± 1 °C after reaction for 6 h under an initial ozone concentration of 45 ± 2 ppm, a relative humidity of 30 ± 2%, and a space velocity of 660 000 h^-1. This showed that this catalyst was far superior to manganese oxide catalysts reported to date. Furthermore, the research results also showed that the catalytic activity of Na-OMS-2 deactivated by the accumulation of oxygen-related intermediates was recovered by calcination at 425 °C under N₂ atmosphere for 0.5 h. Finally, a complete mechanism for ozone decomposition, catalyst deactivation, and regeneration was proposed.

Na+/Vacancy Disordered P2-Na0.67Co1-xTixO2: High-Energy and High-Power Cathode Materials for Sodium Ion Batteries

Although sodium ion batteries (NIBs) have gained wide interest, their poor energy density poses a serious challenge for their practical applications. Therefore, high-energy-density cathode materials are required for NIBs to enable the utilization of a large amount of reversible Na ions. This study presents a P2-type Na_0.67Co_1-xTi_xO₂ (x < 0.2) cathode with an extended potential range higher than 4.4 V to present a high specific capacity of 166 mAh g^-1. A group of P2-type cathodes containing various amounts of Ti is prepared using a facile synthetic method. These cathodes show different behaviors of the Na⁺/vacancy ordering. Na_0.67CoO₂ suffers severe capacity loss at high voltages due to irreversible structure changes causing serious polarization, while the Ti-substituted cathodes have long credible cycleability as well as high energy. In particular, Na_0.67Co_0.90Ti_0.10O₂ exhibits excellent capacity retention (115 mAh g^-1) even after 100 cycles, whereas Na_0.67CoO₂ exhibits negligible capacity retention (<10 mAh g^-1) at 4.5 V cutoff conditions. Na_0.67Co_0.90Ti_0.10O₂ also exhibits outstanding rate capabilities of 108 mAh g^-1 at a current density of 1000 mA g^-1 (7.4 C). Increased sodium diffusion kinetics from mitigated Na⁺/vacancy ordering, which allows high Na⁺ utilization, are investigated to find in detail the mechanism of the improvement by combining systematic analyses comprising TEM, in situ XRD, and electrochemical methods.

Two-Dimensional Metal Oxide Nanomaterials for Next-Generation Rechargeable Batteries

The exponential increase in research focused on two-dimensional (2D) metal oxides has offered an unprecedented opportunity for their use in energy conversion and storage devices, especially for promising next-generation rechargeable batteries, such as lithium-ion batteries (LIBs) and sodium-ion batteries (NIBs), as well as some post-lithium batteries, including lithium-sulfur batteries, lithium-air batteries, etc. The introduction of well-designed 2D metal oxide nanomaterials into next-generation rechargeable batteries has significantly enhanced the performance of these energy-storage devices by providing higher chemically active interfaces, shortened ion-diffusion lengths, and improved in-plane carrier-/charge-transport kinetics, which have greatly promoted the development of nanotechnology and the practical application of rechargeable batteries. Here, the recent progress in the application of 2D metal oxide nanomaterials in a series of rechargeable LIBs, NIBs, and other post lithium-ion batteries is reviewed relatively comprehensively. Current opportunities and future challenges for the application of 2D nanomaterials in energy-storage devices to achieve high energy density, high power density, stable cyclability, etc. are summarized and outlined. It is believed that the integration of 2D metal oxide nanomaterials in these clean energy devices offers great opportunities to address challenges driven by increasing global energy demands.

Amorphous FeF3/C nanocomposite cathode derived from metal–organic frameworks for sodium ion batteries

A cathode of FeF₃/C nanocomposites has been fabricated by a simple vapor-solid fluoridation route which shows superior Na-ion storage performance.

Structural transformation during Li/Na insertion and theoretical cyclic voltammetry of the δ-NH4V4O10 electrode: a first-principles study

A double layer δ-NH₄V₄O₁₀, due to its high energy storage capacity and excellent rate capability, is a very promising cathode material for Li-ion and Na-ion batteries for large-scale renewable energy storage in transportation and smart grids.

Recent Advances and Prospects of Cathode Materials for Sodium-Ion Batteries

Sodium-ion batteries (SIBs) receive significant attention for electrochemical energy storage and conversion owing to their wide availability and the low cost of Na resources. However, SIBs face challenges of low specific energy, short cycling life, and insufficient specific power, owing to the heavy mass and large radius of Na(+) ions. As an important component of SIBs, cathode materials have a significant effect on the SIB electrochemical performance. The most recent advances and prospects of inorganic and organic cathode materials are summarized here. Among current cathode materials, layered transition-metal oxides achieve high specific energies around 600 mW h g(-1) owing to their high specific capacities of 180-220 mA h g(-1) and their moderate operating potentials of 2.7-3.2 V (vs Na(+) /Na). Porous Na3 V2 (PO4 )3 /C nanomaterials exhibit excellent cycling performance with almost 100% retention over 1000 cycles owing to their robust structural framework. Recent emerging cathode materials, such as amorphous NaFePO4 and pteridine derivatives show interesting electrochemical properties and attractive prospects for application in SIBs. Future work should focus on strategies to enhance the overall performance of cathode materials in terms of specific energy, cycling life, and rate capability with cationic doping, anionic substitution, morphology fabrication, and electrolyte matching.

A quinary layer transition metal oxide of NaNi1/4Co1/4Fe1/4Mn1/8Ti1/8O2 as a high-rate-capability and long-cycle-life cathode material for rechargeable sodium ion batteries

A well-crystallized single-phase quinary layer transition metal oxide of NaNi1/4Co1/4Fe1/4Mn1/8Ti1/8O2 was successfully synthesized. It exhibited excellent cycle performance and high rate capability as a cathode material for sodium-ion batteries.