New Insight into Ethylenediaminetetraacetic Acid Tetrasodium Salt as a Sacrificing Sodium Ion Source for Sodium-Deficient Cathode Materials for Full Cells

Presodiation technology: progress, strategy and prospects of sacrificial cathode additives in sodium-based energy storage systems

Presodiation technology plays a pivotal role in enhancing the reversible cycle capacity and initial coulomb efficiency (ICE) of sodium-based energy storage systems (SESSs) by pre-supplementing active sodium ions in the electrode materials, which is crucial for the practical application of SESSs. This technology encompasses various methods, including direct contact presodiation (DC), electrochemical presodiation (EC), chemical presodiation, sodium-rich cathode materials presodiation and sacrificial cathode additive (SCA) presodiation. However, the first four methods encounter specific challenges such as safety concerns, complex procedures, high costs or low irreversible capacity, which significantly impede their industrialization progress. In contrast, the SCA method distinguishes itself with its enhanced safety, straightforward operation, low cost, and superior irreversible specific capacity. More importantly, this method demonstrates excellent compatibility with existing methods of constructing SESS, delivering significant potential for industrialization. Herein, this review summarizes the latest research advancements in SCA presodiation technology, with a particular emphasis on optimizing strategies for some close "ideal" SCA enhancement. The aim of this review is to deepen the understanding of SCA presodiation technology and to offer guidance for the commercial application of high energy density SESSs.

Molecular Engineering Strategies for Organic Pre-Sodiation: Progress and Challenges

Pre-sodiation, which is capable of supplying additional active sodium sources to sodium-ion batteries (SIBs), has been widely accepted as one of the most promising approaches to address the issue of active sodium loss during initial charging and subsequent cycling. Organic materials, with their design flexibility and abundant sources, are well-suited for large-scale applications. To achieve effective organic pre-sodiation, precise control over reaction potential is essential. In view of this, molecular engineering strategies are developed to mediate the pre-sodiation potential of organic materials for efficient pre-sodiation. Nevertheless, a comprehensive review of molecular engineering in organic pre-sodiation is still lacking. This timely review aims to present the crucial role of molecular engineering in organic pre-sodiation and provide an up-to-date overview of this field. After the showcasing of fundamental details of molecular engineering in organic pre-sodiation, recent advances in modifying oxidation decomposition/reduction potentials of organic pre-sodiation materials are briefly introduced, with a focus on the structure-activity relationship between functional group modifications and pre-sodiation potential. Future challenges and directions for developing next-generation organic pre-sodiation technologies are also reviewed. The current review provides important insights into molecular engineering in organic pre-sodiation, guiding the development of next-generation technologies of SIBs.

In-Depth Understanding of Interfacial Na+ Behaviors in Sodium Metal Anode: Migration, Desolvation, and Deposition

Interfacial Na+ behaviors of sodium (Na) anode severely threaten the stability of sodium-metal batteries (SMBs). This review systematically and in-depth discusses the current fundamental understanding of interfacial Na+ behaviors in SMBs including Na+ migration, desolvation, diffusion, nucleation, and deposition. The key influencing factors and optimization strategies of these behaviors are further summarized and discussed. More importantly, the high-energy-density anode-free sodium metal batteries (AFSMBs) are highlighted by addressing key issues in the areas of limited Na sources and irreversible Na loss. Simultaneously, recent advanced characterization techniques for deeper insights into interfacial Na+ deposition behavior and composition information of SEI film are spotlighted to provide guidance for the advancement of SMBs and AFSMBs. Finally, the prominent perspectives are presented to guide and promote the development of SMBs and AFSMBs.

Sodium compensation: a critical technology for transforming batteries from sodium-starved to sodium-rich systems

Sodium-ion batteries (SIBs) have attracted wide attention from academia and industry due to the low cost and abundant sodium resources. Despite the rapid industrialization development of SIBs, it still faces problems such as a low initial coulombic efficiency (ICE) leading to a significant decrease in battery energy density (e.g., 20%). Sodium compensation technology (SCT) has emerged as a promising strategy to effectively increase the ICE to 100% and drastically boost battery cycling performance. In this review, we emphasize the importance of SCT in high-performance SIBs and introduce its working principle. The up-to-date advances in different SCTs are underlined in this review. In addition, we elaborate the current merits and demerits of different SCTs. This review also provides insights into possible future research directions in SCT for high-energy SIBs.

Carbonyl Chemistry for Advanced Electrochemical Energy Storage Systems

On the basis of the sustainable concept, organic compounds and carbon materials both mainly composed of light C element have been regarded as powerful candidates for advanced electrochemical energy storage (EES) systems, due to theie merits of low cost, eco-friendliness, renewability, and structural versatility. It is investigated that the carbonyl functionality as the most common constituent part serves a crucial role, which manifests respective different mechanisms in the various aspects of EES systems. Notably, a systematical review about the concept and progress for carbonyl chemistry is beneficial for ensuring in-depth comprehending of carbonyl functionality. Hence, a comprehensive review about carbonyl chemistry has been summarized based on state-of-the-art developments. Moreover, the working principles and fundamental properties of the carbonyl unit have been discussed, which has been generalized in three aspects, including redox activity, the interaction effect, and compensation characteristic. Meanwhile, the pivotal characterization technologies have also been illustrated for purposefully studying the related structure, redox mechanism, and electrochemical performance to profitably understand the carbonyl chemistry. Finally, the current challenges and promising directions are concluded, aiming to afford significant guidance for the optimal utilization of carbonyl moiety and propel practicality in EES systems.

Injecting Excess Na into a P2-Type Layered Oxide Cathode to Achieve Presodiation in a Na-Ion Full Cell

The initial Na loss limits the theoretical specific capacity of cathodes in Na-ion full cell applications, especially for Na-deficient P2-type cathodes. In this study, we propose a presodiation strategy for cathodes to compensate for the initial Na loss in Na-ion full cells, resulting in a higher specific capacity and a higher energy density. By employing an electrochemical presodiation approach, we inject 0.32 excess active Na into P2-type Na_0.67Li_0.1Fe_0.37Mn_0.53O₂ (NLFMO), aiming to compensate for the initial Na loss in hard carbon (HC) and the inherent Na deficiency of NLFMO. The structure of the NLFMO cathode converts from P2 to P'2 upon active Na injection, without affecting subsequent cycles. As a result, the HC||NLFMO_preNa full cell exhibits a specific capacity of 125 mAh/g, surpassing the value of 61 mAh/g of the HC||NLFMO full cell without presodiation due to the injected active Na. Moreover, the presodiation effect can be achieved through other engineering approaches (e.g., Na-metal contact), suggesting the scalability of this methodology.

Recent Advances in Layered Metal-Oxide Cathodes for Application in Potassium-Ion Batteries

To meet future energy demands, currently, dominant lithium-ion batteries (LIBs) must be supported by abundant and cost-effective alternative battery materials. Potassium-ion batteries (KIBs) are promising alternatives to LIBs because KIB materials are abundant and because KIBs exhibit intercalation chemistry like LIBs and comparable energy densities. In pursuit of superior batteries, designing and developing highly efficient electrode materials are indispensable for meeting the requirements of large-scale energy storage applications. Despite using graphite anodes in KIBs instead of in sodium-ion batteries (NIBs), developing suitable KIB cathodes is extremely challenging and has attracted considerable research attention. Among the various cathode materials, layered metal oxides have attracted considerable interest owing to their tunable stoichiometry, high specific capacity, and structural stability. Therefore, the recent progress in layered metal-oxide cathodes is comprehensively reviewed for application to KIBs and the fundamental material design, classification, phase transitions, preparation techniques, and corresponding electrochemical performance of KIBs are presented. Furthermore, the challenges and opportunities associated with developing layered oxide cathode materials are presented for practical application to KIBs.

Electronic Effect and Regiochemistry of Substitution in Pre-sodiation Chemistry

The low oxidation potential of a pre-sodiation cathode additive intrinsically prevents decomposition of the electrolyte. Although the introduction of electron-donating substitution reduces the oxidation potential, the additional molecular weight restricts the output capacity. Herein, as theroretically predicted, the electrochemical oxidation potential of sodium carboxylate is manipulated by the electronic effect and regiochemistry of the functionality, in which the stronger electron-donating substituent, p-π conjugation, and optimized regiochemistry can dramatically lead to the lower potential originated from the elevation of the highest occupied molecular orbital level. Thus, benefiting from the para-NH₂ unit accompanied by a conjugated aromatic architecture, molecularly engineered sodium para-aminobenzoate (PABZ-Na) presents a reduced oxidation plateau of 3.45 V. Triggered by the positive compensation merit, sodium-based electrochemical storage systems manifest excellent electrochemical performances. This breakthrough sheds light into the correlation between the electronic effect of the functional group and the oxidation potential of the organic additive, affording in-depth insights into the fundamental guidance of pre-sodiation chemistry.

Molecularly Compensated Pre-Metallation Strategy for Metal-Ion Batteries and Capacitors

The use of a sacrificial cathode additive as a pre-metallation method could ensure adequate metal sources for advanced energy storage devices. However, this pre-metallation technique suffers from the precise regulation of decomposition potential of additive. Herein, a molecularly compensated pre-metallation (Li/Na/K) strategy has been achieved through Kolbe electrolysis, in which the electrochemical oxidation potential of a metal carboxylate is manipulated by the bonding energy of the oxygen-metal (O-M) moiety. The electron-donating effect of the substituent and the low charge density of the cation can dramatically weaken the O-M bond strength, further bringing out the reduced potential. Thus, sodium acetate exhibits a superior pre-sodiation feature for sodium-ion battery accompanied with a large irreversible specific capacity of 301.8 mAh g^-1 , remarkably delivering 70.6 % enhanced capacity retention in comparison to the additive-free system after 100 cycles. This methodology has been extended to construct a high-performance lithium-ion battery and a lithium/sodium/potassium-ion capacitor.

Insights on Electrochemical Behaviors of Sodium Peroxide as a Sacrificial Cathode Additive for Boosting Energy Density of Na-Ion Battery

The development of Na-ion full cells (NIFCs) suffers from the issue that the solid electrolyte interphase formation on the carbon anode consumes the limited sodium from cathode and thus incurs the decreased energy density and poor cyclic stability. To address these issues, we herein report that Na₂O₂ could be used as a sacrificial Na source through spraying its slurry on the surface of cathode, and investigate its stability as well as electrochemical behavior toward NIFCs. The results show that Na₂O₂ has good chemical and storage stability under a dry atmosphere and has no negative effect on the electrochemical performance of the cathode. Compared with the pristine cathode, the Na₂O₂-decorated cathode exhibits higher discharge capacity, superior capacity retention, and rate capability in a full cell with a carbon anode. Our cathode Na compensation strategy provides an effective avenue to make up for the irreversible Na⁺ loss cause by the formation of solid electrolyte interphase on the anode, thereby promoting the electrochemical performance and energy density of NIFCs toward the large-scale application.

Sodium citrate as a self-sacrificial sodium compensation additive for sodium-ion batteries

Commercial sodium citrate is proposed as the self-sacrificial cathode additive for the first time to offset the initial sodium loss. The optimum additive can obviously increase the energy density of the as-constructed hard carbon//Na3V2(PO4)2F3/rGO full-cell by 28.9% without sacrificing its other electrochemical properties, showing promising application prospects in sodium ion batteries.

Eutectic Synthesis of the P2-Type NaxFe1/2Mn1/2O2 Cathode with Improved Cell Design for Sodium-Ion Batteries

An engaging area of research in sodium-ion batteries (SIBs) has been focusing on discovery, design, and synthesis of high-capacity cathode materials in order to boost energy density to levels close enough to that of state-of-the-art lithium-ion batteries. Of particular interest, P2-type layered oxide, Na_2/3Fe_1/2Mn_1/2O₂, has been researched as a potential cathode in SIBs based on its high theoretical capacity of 260 mA h/g and use of noncritical materials. However, the reported synthesis methods are not only complex and energy-demanding but also often yield inhomogeneous and impure materials with capacities less than 200 mA h/g under impractical test conditions. Here, we report a novel synthesis route using low-temperature eutectic reaction to produce highly homogeneous, crystalline, and impurity-free P2-Na_xFe_1/2Mn_1/2O₂ with enhanced Na-ion diffusivity and kinetics. The overall electrochemical performances of the Na-ion cells have been improved by pairing the P2-cathode with presodiated hard carbon anodes, leading to reversible capacities in the range of 180 mA h/g. This new approach is a contribution toward the simplification of synthesis and scalability of sodium-based cathodes with high crystallinity and fine-tuned morphology and the realization of a sodium-ion battery system with lower cost and improved electrochemical performance.