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The anode/electrolyte interface behavior, and by extension, the overall cell performance of sodium‐ion batteries is determined by a complex interaction of processes that occur at all components of the electrochemical cell across a wide range of size‐ and timescales. Single‐scale studies may provide incomplete insights, as they cannot capture the full picture of this complex and intertwined behavior. Broad, multiscale studies are essential to elucidate these processes. Within this perspectives article, several analytical and theoretical techniques are introduced, and described how they can be combined to provide a more complete and comprehensive understanding of sodium‐ion battery (SIB) performance throughout its lifetime, with a special focus on the interfaces of hard carbon anodes. These methods target various length‐ and time scales, ranging from micro to nano, from cell level to atomistic structures, and account for a broad spectrum of physical and (electro)chemical characteristics. Specifically, how mass spectrometric, microscopic, spectroscopic, electrochemical, thermodynamic, and physical methods can be employed to obtain the various types of information required to understand battery behavior will be explored. Ways are then discussed how these methods can be coupled together in order to elucidate the multiscale phenomena at the anode interface and develop a holistic understanding of their relationship to overall sodium‐ion battery function. [ABSTRACT FROM AUTHOR]

Electrolytes play a crucial role in facilitating the ionic movement between cathode and anode, which is essential for the flow of electric current during the charging and discharging process of the rechargeable batteries. In particular, electrolyte additives are considered as effective and economical approaches into the advancements of the battery technologies in both the conventional non‐aqueous and burgeoning aqueous electrolyte systems. Herein, a systematic and comprehensive review of the electrolyte additives is reported for the interfacial engineering of Li and Zn metal anodes in the non‐aqueous and aqueous electrolytes, respectively. The types of electrolyte additives and their corresponding functionalities for the protection of these two metal anodes are discussed along with the electrochemical features of solid electrolyte interphase (SEI) derived from electrolyte additives. The recent progress on electrolyte additives for these two battery systems are also addressed from the perspectives of electrode, electrolyte, and the associated SEI. Finally, the outlook and perspective on the current issues and future directions in the field of electrolyte additive engineering are presented for next‐generation battery technologies beyond the conventional Li‐ion batteries. [ABSTRACT FROM AUTHOR]

The mechanically and electrochemically stable and ionically conducting solid electrolyte interphase (SEI) is important for the stabilization of metal anodes. Since SEIs are originally absent in aqueous zinc metal batteries (AZMBs), it is very challenging to suppress water‐induced side reactions and dendrite growth of Zn metal anodes (ZMAs). Herein, a gradient‐structured and robust solid gradient SEI, consisting of B,O‐inner and F,O‐exterior layer, in situ formed by hydrated eutectic electrolyte for the homogeneous and reversible Zn deposition, is demonstrated. Moreover, the molar ratio of acetamide to Zn salt is modulated to prohibit the water activity and the hydrolysis of BF4− as well as to achieve high ionic conductivity owing to the regulation of the solvation sheath of Zn2+. Consequently, the eutectic electrolyte allows Zn||Zn symmetric cells to achieve a cycling lifespan of over 4400 h at 0.5 mA cm−2 as well as Zn||PANI full cells to deliver a high capacity retention of 73.2% over 4000 cycles at 1 A g−1 and to demonstrate the stable operation at low temperatures. This work provides the rational design for the hydrated eutectic electrolyte and the corresponding gradient SEIs for dendrite‐free and stable Zn anodes even under harsh conditions. [ABSTRACT FROM AUTHOR]

It remains a challenge to design aqueous electrolytes to secure the complete reversibility of zinc metal anodes. The concentrated water‐in‐salt electrolytes, e.g., 30 m ZnCl2, are promising candidates to address the challenges of the Zn metal anode. However, the pure 30 m ZnCl2 electrolyte fails to deliver a smooth surface morphology and a practically relevant Coulombic efficiency. Herein, it is reported that a small concentration of vanillin, 5 mg mLwater−1, added to 30 m ZnCl2 transforms the reversibility of Zn metal anode by eliminating dendrites, lowering the Hammett acidity, and forming an effective solid electrolyte interphase. The presence of vanillin in the electrolyte enables the Zn metal anode to exhibit a high Coulombic efficiency of 99.34% at a low current density of 0.2 mA cm−2, at which the impacts of the hydrogen evolution reaction are allowed to play out. Using this new electrolyte, a full cell Zn metal battery with an anode/cathode capacity (N/P) ratio of 2:1 demonstrates no capacity fading over 800 cycles. [ABSTRACT FROM AUTHOR]

Lithium‐ion batteries (LIBs) have transformed the use of mobile electronics and storage technologies. Alongside advances in materials, an in‐depth understanding of the interfacial phenomena and interphase formation mechanisms in LIBs is crucial. Interphases are widely recognized as the most important and the least understood components of LIBs and play a direct role in defining cell performance, cyclability, and safety. This article presents a review of recent developments in vibrational spectroscopy techniques of Raman, infrared, and sum‐frequency generation spectroscopies to probe the fundamental aspects of interphases on the anode and cathode of LIBs. First the vibrational spectroscopy techniques and their relevant technical considerations for interphase characterization are briefly introduced. In the next step, the latest studies on the fundamental properties, composition, and structure of interphases employing vibrational spectroscopy techniques are presented. This review focuses on in situ/operando investigations; however, post‐mortem studies are also discussed briefly. [ABSTRACT FROM AUTHOR]

Challenges from high‐energy‐density storage applications have boosted the pursuit of designing high‐rate and low‐temperature lithium (Li) metal batteries (LMBs). Formulating high‐concentration electrolytes (HCEs) with a high transference number (t+) is an alternative solution to satisfy these demands. However, the implementation of HCEs is impeded by their lower ionic conductivity, higher viscosity, poorer wettability, and higher melting point, which are harmful to the practical applications. Herein, an anionic coordination manipulation strategy is proposed to break the constraints presented by HCEs. By manipulating the anionic species with different coordinating abilities, a high t+ up to 0.9 can be achieved even in the low‐concentration electrolytes of 1 mol L−1. By further forming a multilayer solvation structure in the anion manipulated electrolyte using non‐polar diluents, high Li Coulombic efficiency superior to 99% can be maintained under a high current density of 3 mA cm−2, and much‐improved performance is also demonstrated in high‐loading Li metal pouch cells. Furthermore, when applying multilayer solvated structure in electrolyte engineering, Li metal anodes at subzero temperature and LMBs at 0 °C also exhibit impressive cycling stability. This work provides a new guideline for designing advanced electrolytes for high‐rate LMBs under practical conditions. [ABSTRACT FROM AUTHOR]

As anodes for metal‐ion batteries, metal phosphides usually suffer from severe capacity degradation because of their huge volume expansion and unstable solid electrolyte interphase (SEI), especially for potassium‐ion batteries (PIBs). To address these issues, this study proposes amorphous phosphates acting as buffer materials. Ten types of metal phosphide composites embedded with in situ‐formed amorphous phosphates are prepared by one‐step ball milling using red phosphorus (RP) and the corresponding metal oxides (MOs) as starting materials. A zinc phosphide composite is selected for further study as a PIB anode. Benefitting from the effective suppression of volume variation, a KF‐rich SEI is formed on the electrode surface in the KFSI‐based electrolyte. The zinc phosphide composite exhibits a high reversible specific capacity and outstanding long‐term cycling stability (476 mAh g−1 over 350 cycles at 0.1 A g−1 after going through a rate capability test and 177 mAh g−1 after 6000 cycles at 1.0 A g−1) and thus achieves the best cycling performance among all reported metal phosphide‐based anodes for PIBs. This study highlights a low‐cost and effective strategy to guide the development of metal phosphides as high‐performance anodes for PIBs. [ABSTRACT FROM AUTHOR]

An intrinsic challenge of Li‐ion batteries is the instability of electrolytes against anode materials. For anodes with a favorably low operating potential, a solid‐electrolyte interphase (SEI) formed during initial cycles provides stability, traded off for capacity consumption. The SEI is mainly determined by the anode material, electrolyte composition, and formation conditions. Its properties are typically adjusted by changing the liquid electrolyte's composition. Artificial SEIs (Art‐SEIs) offer much more freedom to address and tune specific properties, such as chemical composition, impedance, thickness, and elasticity. Art‐SEIs for intercalation, alloying, conversion and Li metal anodes have to fulfil varying requirements. In all cases, sufficient transport properties for Li‐ions and (electro‐)chemical stability must be guaranteed. Several approaches for Art‐SEIs preparation have been reported: from simple casting and coating techniques to elaborated Phys‐Chem modifications and deposition processes. This review critically reports on the promising approaches for Art‐SEIs formation on different type of anode materials, focusing on methodological aspects. The specific requirements for each approach and material class, as well as the most effective strategies for Art‐SEI coating, are discussed and a roadmap for further developments towards next‐generation stable anodes are provided. [ABSTRACT FROM AUTHOR]

For sodium (Na)‐rechargeable batteries to compete, and go beyond the currently prevailing Li‐ion technologies, mastering the chemistry and accompanying phenomena is of supreme importance. Among the crucial components of the battery system, the electrolyte, which bridges the highly polarized positive and negative electrode materials, is arguably the most critical and indispensable of all. The electrolyte dictates the interfacial chemistry of the battery and the overall performance, having an influence over the practical capacity, rate capability (power), chemical/thermal stress (safety), and lifetime. In‐depth knowledge of electrolyte properties provides invaluable information to improve the design, assembly, and operation of the battery. Thus, the full‐scale appraisal of both tailored electrolytes and the concomitant interphases generated at the electrodes need to be prioritized. The deployment of large‐format Na‐based rechargeable batteries also necessitates systematic evaluation and detailed appraisal of the safety‐related hazards of Na‐based batteries. Hence, this review presents a comprehensive account of the progress, status, and prospect of various Na+‐ion electrolytes, including solvents, salts and additives, their interphases and potential hazards. [ABSTRACT FROM AUTHOR]

Development of electrolytes that simultaneously have high ionic conductivity, wide electrochemical window, and lithium dendrite suppression ability is urgently required for high‐energy lithium‐metal batteries (LMBs). Herein, an electrolyte is designed by adding a countersolvent into LiFSI/DMC (lithium bis(fluorosulfonyl)amide/dimethyl carbonate) electrolytes, forming countersolvent electrolytes, in which the countersolvent is immiscible with the salt but miscible with the carbonate solvents. The solvation structure and unique properties of the countersolvent electrolyte are investigated by combining electroanalytical technology with a Molecular Dynamics simulation. Introducing the countersolvent alters the coordination shell of Li+ cations and enhances the interaction between Li+ cations and FSI− anions, which leads to the formation of a LiF‐rich solid electrolyte interphase, arising from the preferential reduction of FSI− anions. Notably, the countersolvent electrolyte suppresses Li dendrites and enables stable cycling performance of a Li||NCM622 battery at a high cut‐off voltage of 4.6 V at both 25 and 60 °C. This study provides an avenue to understand and design electrolytes for high‐energy LMBs in the future. [ABSTRACT FROM AUTHOR]

In the article "Vanillin: An Effective Additive to Improve the Longevity of Zn Metal Anode in a 30 m ZnCl2 Electrolyte," researchers P. Alex Greaney, Xiulei Ji, and their colleagues discuss the challenges of designing aqueous electrolytes for zinc metal anodes in batteries. They found that adding a small amount of vanillin to a 30 m ZnCl2 electrolyte improves the reversibility of the anode, prevents dendrite formation, and increases Coulombic efficiency. This electrolyte formulation allows for stable cycling of a zinc metal battery with an N/P ratio of 2 for over 800 cycles. [Extracted from the article]

Abstract: Potassium‐ion batteries (PIBs) are promising energy storage systems because of the abundance and low cost of potassium. The formidable challenge is to develop suitable electrode materials and electrolytes for accommodating the relatively large size and high activity of potassium. Herein, Bi‐based materials are reported as novel anodes for PIBs. Nanostructural design and proper selection of the electrolyte salt have been used to achieve excellent cycling performance. It is found that the potassiation of Bi undergoes a solid‐solution reaction, followed by two typical two‐phase reactions, corresponding to Bi ↔ Bi(K) and Bi(K) ↔ K5Bi4 ↔ K3Bi, respectively. By choosing potassium bis(fluorosulfonyl)imide (KFSI) to replace potassium hexafluorophosphate (KPF6) in carbonate electrolyte, a more stable solid electrolyte interphase layer is achieved and results in notably enhanced electrochemical performance. More importantly, the KFSI salt is very versatile and can significantly promote the electrochemical performance of other alloy‐based anode materials, such as Sn and Sb. [ABSTRACT FROM AUTHOR]

Use of a protective coating on a lithium metal anode (LMA) is an effective approach to enhance its coulombic efficiency and cycling stability. Here, a facile approach to produce uniform silver nanoparticle‐decorated LMA for high‐performance Li metal batteries (LMBs) is reported. This effective treatment can lead to well‐controlled nucleation and the formation of a stable solid electrolyte interphase (SEI). Ag nanoparticles embedded in the surface of Li anodes induce uniform Li plating/stripping morphologies with reduced overpotential. More importantly, cross‐linked lithium fluoride‐rich interphase formed during Ag+ reduction enables a highly stable SEI layer. Based on the Ag‐LiF decorated anodes, LMBs with LiNi1/3Mn1/3Co1/3O2 cathode (≈1.8 mAh cm−2) can retain >80% capacity over 500 cycles. The similar approach can also be used to treat sodium metal anodes. Excellent stability (80% capacity retention in 10 000 cycles) is obtained for a Na||Na3V2(PO4)3 full cell using a Na‐Ag‐NaF/Na anode cycled in carbonate electrolyte. These results clearly indicate that synergetic control of the nucleation and SEI is an efficient approach to stabilize rechargeable metal batteries. [ABSTRACT FROM AUTHOR]

In article number 1802912, Zhe Peng, Chuying Ouyang, Deyu Wang and co‐workers report an interesting feature of SEI‐functionalized artificial layers, derived from a LiF decorated carbon layered structure. Surface chemistry and modeling analysis give evidence of a special conversion of LiF into C‐Fx surface components on defective carbon sheets during Li plating, and the as‐formed SEI‐functionalized layer can retard electron transfer by three orders of magnitude to avoid undesirable Li deposition on the top surface, and ameliorates Li+ ion migration to enable uniform and dendrite‐free Li deposition beneath such an interlayer. [ABSTRACT FROM AUTHOR]

Lithium (Li) metal is a key anode material for constructing next generation high energy density batteries. However, dendritic Li deposition and unstable solid electrolyte interphase (SEI) layers still prevent practical application of Li metal anodes. In this work, it is demonstrated that an uniform Li coating can be achieved in a lithium fluoride (LiF) decorated layered structure of stacked graphene (SG), leading to the formation of an SEI‐functionalized membrane that retards electron transfer by three orders of magnitude to avoid undesirable Li deposition on the top surface, and ameliorates Li+ ion migration to enable uniform and dendrite‐free Li deposition beneath such an interlayer. Surface chemistry analysis and density functional theory calculations demonstrate that these beneficial features arise from the formation of C–Fx surface components on the SG sheets during the Li coating process. Based on such an SEI‐functionalized membrane, stable cycling at high current densities up to 3 mA cm−2 and Li plating capacities up to 4 mAh cm−2 can be realized in LiPF6/carbonate electrolytes. This work elucidates the promising strategy of modifying Li plating behavior through the SEI‐functionalized carbon structure, with significantly improved cycling stability of rechargeable Li metal anodes. A surface conversion of LiF into C–Fx components on a defective carbon sheet can be achieved during Li plating to provide a solid electrolyte interphase (SEI)‐functionalization of a layered carbon structure. Uniform Li deposition with dendrite‐free features can be realized beneath the SEI‐functionalized layer for significantly improved cycling stability of Li metal anodes. [ABSTRACT FROM AUTHOR]

Lithium (Li) metal anodes have long been counted on to meet the increasing demand for high energy, high‐power rechargeable battery systems but they have been plagued by uncontrollable plating, unstable solid electrolyte interphase (SEI) formation, and the resulting low Coulombic efficiency. These problems are even aggravated under commercial levels of current density and areal capacity testing conditions. In this work, the channel‐like structure of a carbonized eggplant (EP) as a stable "host" for Li metal melt infusion, is utilized. With further interphase modification of lithium fluoride (LiF), the as‐formed EP–LiF composite anode maintains ≈90% Li metal theoretical capacity and can successfully suppress dendrite growth and volume fluctuation during cycling. EP–LiF offers much improved symmetric cell and full‐cell cycling performance with lower and more stable overpotential under various areal capacity and elevated rate capability. Furthermore, carbonized EP serves as a light‐weight high‐performance current collector, achieving an average Coulombic efficiency ≈99.1% in ether‐based electrolytes with 2.2 mAh cm−2 cycling areal capacity. The natural structure of carbonized EP will inspire further artificial designs of electrode frameworks for both Li anode and sulfur cathodes, enabling promising candidates for next‐generation high‐energy density batteries. An interconnected channel‐like framework originating from eggplant is introduced to serve as a stable host for lithium (Li) metal anodes. Coulombic efficiency of 99.1% is achieved when directly using the framework as current collector. Minimal volume fluctuation, suppressed dendrite growth, and improved rate capability are realized when Li metal is melt infiltrated into the framework to form a composite anode. [ABSTRACT FROM AUTHOR]