Aqueous Al-ion batteries (AAIBs) are the subject of great interest due to the inherent safety and high theoretical capacity of aluminum. The high abundancy and easy accessibility of aluminum raw materials further make AAIBs appealing for grid-scale energy storage. However, the passivating oxide film formation and hydrogen side reactions at the aluminum anode as well as limited availability of the cathode lead to low discharge voltage and poor cycling stability. Here, we proposed a new AAIB system consisting of an Al x MnO 2 cathode, a zinc substrate-supported Zn−Al alloy anode, and an Al(OTF) 3 aqueous electrolyte. Through the in situ electrochemical activation of MnO, the cathode was synthesized to incorporate a two-electron reaction, thus enabling its high theoretical capacity. The anode was realized by a simple deposition process of Al 3+ onto Zn foil substrate. The featured alloy interface layer can effectively alleviate the passivation and suppress the dendrite growth, ensuring ultralong-term stable aluminum stripping/ plating. The architected cell delivers a record-high discharge voltage plateau near 1.6 V and specific capacity of 460 mAh g −1 for over 80 cycles. This work provides new opportunities for the development of highperformance and low-cost AAIBs for practical applications.

Voltage fade prevents effective use of the excess capacity and represents the most crucial technical challenge faced by Li-and Mn-rich cathode materials (LMR) in modern batteries.Although oxygen release has been arguably considered as an initiator for the failure mechanism, its prerequisite driving force has yet to be fully understood. Herein, relying on the in-situ nanoscale sensitive coherent X-ray diffraction imaging (BCDI) technique, we are able to track the dynamic structure evolution of the LMR cathode. The results, surprisingly, reveal that continuous nanostrain accumulation arose from lattice displacement in nano-domain structures during cell operation is the original driving force for detrimental structure degradations together with oxygen loss that triggers the well-known rapid voltage decay in LMR. By further leveraging primary to multi-particle structure and electrode-level as well as atomic scale observations, we demonstrate that the heterogeneous nature of the LMR cathode inevitably causes pernicious phase displacement which cannot be eliminated by the previous trials. With these fundamental discoveries, we propose the structural design strategy to mitigate the lattice displacement and inhomogeneous electrochemical/structural evolutions, thereby achieving stable voltage and capacity profiles. These findings highlight the significance of lattice displacement in voltage decay mechanism and will inspire a wave of efforts to unlock the potential of the broad-scale commercialization of LMR cathode material.

3.8 V (vs Li + /Li), making them a class of promising cathode material and attracting considerable attention. Nevertheless, the inferior cycling stability and poor rate capability of Ni-rich oxide cathode materials have to be overcome before they can compete in practical implementation. [2,4] These drawbacks are largely attributed to their spherical micrometer-sized secondary particles aggregated densely by many randomly oriented primary nanoparticles, [4][5][6] as shown in Figure 1a. On the one hand, concomitant with this structure, the surface of secondary particles is terminated with random crystal planes. As Li + can only diffuse along the 2D {010} plane in the hexagonal-layer structure of NCM materials, [4,7] the randomly exposed crystal planes (not solely the active {010} plane) may substantially hinder the Li + exchange at the electrode/electrolyte interface. Meanwhile, the randomly oriented primary nanoparticles induce a prolonged and mazy Li + diffusion pathway inside the secondary particles, because Li + ions have to migrate across the grain boundaries, especially between the grains with inconsistent crystal planes. On the other hand, the successive phase transition accompanied by repeated Li + insertion/extraction would result in anisotropic variation of the lattice parameters, and such variation is severely aggravated with the increase of Ni content. [8] Accordingly, in the Ni-rich oxide cathode materials, the substantial anisotropic lattice expansion/contraction would result in drastic microstrains at the boundaries of randomly oriented primary particles due to the asynchronous volume Ni-rich Li[Ni x Co y Mn 1−x−y ]O 2 (x ≥ 0.8) layered oxides are the most promising cathode materials for lithium-ion batteries due to their high reversible capacity of over 200 mAh g −1 . Unfortunately, the anisotropic properties associated with the α-NaFeO 2 structured crystal grains result in poor rate capability and insufficient cycle life. To address these issues, a micrometersized Ni-rich LiNi 0.8 Co 0.1 Mn 0.1 O 2 secondary cathode material consisting of radially aligned single-crystal primary particles is proposed and synthesized. Concomitant with this unique crystallographic texture, all the exposed surfaces are active {010} facets, and 3D Li + ion diffusion channels penetrate straightforwardly from surface to center, remarkably improving the Li + diffusion coefficient. Moreover, coordinated charge-discharge volume change upon cycling is achieved by the consistent crystal orientation, significantly alleviating the volume-change-induced intergrain stress. Accordingly, this material delivers superior reversible capacity (203.4 mAh g −1 at 3.0-4.3 V) and rate capability (152.7 mAh g −1 at a current density of 1000 mA g −1 ). Further, this structure demonstrates excellent cycling stability without any degradation after 300 cycles. The anisotropic morphology modulation provides a simple, efficient, and scalable way to boost the performance and applicability of Ni-rich layered oxide cathode materials.

Layered transition metal oxides have drawn much attention as a promising candidate cathode material for sodium‐ion batteries. However, their performance degradation originating from strains and lattice phase transitions remains a critical challenge. Herein, a high‐concentration Zn‐substituted NaxMnO2 cathode with strongly suppressed P2–O2 transition is investigated, which exhibits a volume change as low as 1.0% in the charge/discharge process. Such ultralow strain characteristics ensure a stable host for sodium ion storage, which significantly improves the cycling stability and rate capability of the cathode material. Also, the strong coupling between the highly reversible capacity and the doping content of Zn in NaxMnO2 is investigated. It is suggested that a reversible anionic redox reaction can be effectively triggered by Zn ions and is also highly dependent on the Zn content. Such an ion doping strategy could shed light on the design and construction of stable and high‐capacity sodium ion host.

Luminol-based electrochemiluminescence (ECL) can be readily excited by various reactive oxygen species (ROS) electrogenerated with an oxygen reduction reaction (ORR). However, the multiple active intermediates involved in the ORR catalyzed with complex nanomaterials lead to recognizing the role of ROS still elusive. Moreover, suffering from the absence of the direct electrochemical oxidation of luminol at the cathode and poor transformation efficiency of O2 to ROS, the weak cathodic ECL emission of luminol is often neglected. Herein, owing to the tunable coordination environment and structure-dependent catalytic feature, single-atom catalysts (SACs) are employed to uncover the relationship between the intrinsic ORR activity and ECL behavior. Interestingly, the traditionally negligible cathodic ECL of luminol is first boosted (ca. 70-fold) owing to the combination of electrochemical ORR catalyzed via SACs and chemical oxidation of luminol. The boosted cathodic ECL emission exhibits electron-transfer pathway-dependent response by adjusting the surrounding environment of the center metal atoms in a controlled way to selectively produce different active intermediates. This work bridges the relationship between ORR performance and ECL behavior, which will guide the development of an amplified sensing platform through rational tailoring of the ORR activity of SACs and potential-resolved ECL assays based on the high-efficiency cathodic ECL reported.

Atomically dispersed Fe–N–C materials recently hold great interest in costly Pt substitution for the cathodic oxygen reduction reaction of fuel cells. However, the heat treatment involved in the material preparation excites Fe aggregating into nanosized species with low activity rather than single-atom Fe sites. Herein, we propose a “ceria-assisted” strategy to preferentially generate active single-atom Fe sites in Fe–N–C materials, which involves oxidative polymerization of pyrrole, Ce3+ and Fe3+ adsorption, and subsequent heat treatment. Because of its spatial confinement and strong trapping for Fe atoms, ceria can effectively suppress agglomeration of isolated Fe atoms and stabilize the Fe atoms by bonding to O in the lattice during the heat treatment, leading to a high content of atomically dispersed Fe (4.6 wt %). Accordingly, the final catalyst showed ultrahigh ORR activity with a half-wave potential of 0.915 V and kinetic current density of 7.15 mA cm–2 at 0.9 V. When used at the cathode in anion exchange membrane fuel cell, a maximum power density of 496 mW cm–2 was achieved, which is one of the best performance reported in the literature for Fe–N–C-type electrocatalysts.

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cycle stability. [6][7][8] A bottleneck for high performance in Na batteries is the cathode side in which the specify capacity is lower than 200 mA h g −1 because typical intercalation compound cathodes generally only accommodate one sodium ion per transition metal core. [9,10] In order to enhance energy densities of Na-based batteries, one way is to increase the upper cell reaction voltage limit during charge, [11,12] which is particularly challenging for Na-based battery cathodes due to the lower chemical potentials (2.71 V for Na + /Na vs 3.04 V for Li + /Li, with respect to standard hydrogen electrode). What is more, instability of electrolytes and undesirable side reactions at high voltages also pose additional challenges.The other way to achieve high capacity is to design materials in which more Na ions per metal can be incorporated reversibly. Similar to the lithium-ion system, conversion materials have been expected to be a promising candidate in the sodiumion system because they have the potential to accommodate over one sodium ion in the structure. However, undesirable drawbacks of conversion materials in lithiumion batteries such as poor cycle stability, low reversibility, and large voltage hysteresis also occur in Na-ion batteries. [13,14] Despite decades of research efforts and numerous reports in lithium ion system, the mechanisms underpinning the conversion reactions in sodium batteries, in particular irreversibility and large voltage hysteresis are less understood. [15][16][17] In this work, phase transformation and distribution in sodium-metal sulfide batteries has for the first time been imaged by in operando synchrotron full-field transmission X-ray microscopy (TXM) during multiple charge/discharge cycles. FeS was selected as the model material owing to its representative property and high theoretical capacity (≈610 mA h g −1 ). [18] 2D chemical phase evolution and composition information of FeS are directly mapped by TXM with X-ray absorption near edge structure (XANES) technique, and sodium ion diffusivity is investigated by galvanostatic intermittent titration technique (GITT). 3D microstructural evolution and its quantification are achieved by synchrotron X-ray nanotomography. [8,19,20] Through these approaches, we are able to comprehensively understand the origin of irreversible and large voltage hysteresis in Na-FeS Irreversible electrochemical behavior and large voltage hysteresis are commonly observed in battery materials, in particular for materials reacting through conversion reaction, resulting in undesirable round-trip energy loss and low coulombic efficiency. Seeking solutions to these challenges relies on the understanding of the underlying mechanism and physical origins. Here, this study combines in operando 2D transmission X-ray microscopy with X-ray absorption near edge structure, 3D tomography, and galvanostatic intermittent titration techniques to uncover the conversion reaction in sodium-metal sulfide batteries, a promising high-energy battery system. This study shows a high...