Safety concerns about organic media-based batteries are the key public arguments against their widespread usage. Aqueous batteries (ABs), based on water which is environmentally benign, provide a promising alternative for safe, cost-effective, and scalable energy storage, with high power density and tolerance against mishandling. Research interests and achievements in ABs have surged globally in the past 5 years. However, their large-scale application is plagued by the limited output voltage and inadequate energy density. We present the challenges in AB fundamental research, focusing on the design of advanced materials and practical applications of whole devices. Potential interactions of the challenges in different AB systems are established. A critical appraisal of recent advances in ABs is presented for addressing the key issues, with special emphasis on the connection between advanced materials and emerging electrochemistry. Last, we provide a roadmap starting with material design and ending with the commercialization of next-generation reliable ABs.

efforts have been devoted to mimicking the successful material strategies used for LIBs. This is especially the case regarding suitable electrode materials that enable reversible Na + intercalation and deintercalation. [1,6] In this regard, a series of promising SIB electrode materials has been discovered in the past decade. [7][8][9][10][11][12][13][14] In terms of anode materials, however, the standard graphite anodes in LIBs exhibit extremely limited sodium storage properties. [15,16] Because Na + (1.16 Å) has larger ionic radius than Li + (0.90 Å), [17] which greatly hinders its reversible insertion into and extraction from conventional graphite anodes. Other non-carbon candidates, including transition metal compounds (e.g., oxides, [18] sulfides, [19] and phosphides [20] ) and alloys (e.g., Sn [21] and Sb [22] ) usually suffer from poor cycling durability because of their low intrinsic conductivity and significant volume change, [23] making them being far from real application in SIBs. Therefore, it is very urgent to develop efficient anode materials for advancing SIB systems.Although traditional graphite fails to provide sufficient interlayer spacing (≈0.34 nm) to host larger Na + , [24,25] both experimental results and theoretical calculations show that the energy barrier for Na + insertion into graphite layers can be reduced to a surmountable level once the interlayer distance is increased to 0.37 nm. [24] Accordingly, a rational material design strategy lies in enlarging the carbon interlayer distance to unlock its Na + storage capability. [24,26] To this end, different carbon materials with expanded interlayer spacing have emerged as improved anodes for SIBs. [13,[26][27][28][29] For instance, Wen et al. prepared expanded graphite with an enlarged interlayer distance of 0.43 nm by introducing oxygen-containing functional groups via a two-step oxidation-reduction treatment of graphite. [27] The as-prepared expanded graphite exhibited high reversible capacity, but its rate capability needed to be improved. Notably, among the reported carbon materials, heteroatom (e.g., N, P, and S) doping has also been demonstrated as one of the most effective ways to expand the carbon interlayer distance. [26,28,29] As an example, Hou and coworkers reported large-area carbon nanosheets doped with phosphorus, which achieved an expanded interlayer spacing of 0.42 nm, allowing for highly reversible Na + storage with excellent rate performance and Heteroatom-doped carbon materials with expanded interlayer distance have been widely studied as anodes for sodium-ion batteries (SIBs). However, it remains unexplored to further enlarge the interlayer spacing and reveal the influence of heteroatom doping on carbon nanostructures for developing more efficient SIB anode materials. Here, a series of N-rich few-layer graphene (N-FLG) with tuneable interlayer distance ranging from 0.45 to 0.51 nm is successfully synthesized by annealing graphitic carbon nitride (g-C 3 N 4 ) under zinc catalysis and selected temperature (T = 700, 800, an...

Research interests and achievements in zinc aqueous batteries, such as alkaline Zn//Mn, Zn//Ni/Co, Zn-air batteries and near-neutral Zn ion and hybrid ion batteries, have surged throughout the world due to their peculiarity of low-cost and high-safety. However, practical application of Zn-based secondary batteries is plagued by restrictive energy and power densities in which an inadequate output plateau voltage and sluggish kinetics are mutually accountable. Here, a novel paradigm high-rate and high-voltage Zn-Mn hybrid aqueous battery (HAB) is constructed with an expanded electrochemical stability window over 3.4 V that is affordable. As a proof of concept, we demonstrate catalyzed MnO 2 /Mn 2+ electrolysis kinetics in HAB via facile introduction of Ni 2+ into the electrolyte. Various spectra techniques are employed including, in situ synchrotron X-ray powder diffraction, ex situ X-ray absorption fine structure and electron energy loss spectrum, to reveal the reversible charge storage mechanism and origin of boosted rate-capability. Density functional theory calculations figure out enhanced active electron states and charge delocalization after This article is protected by copyright. All rights reserved.introducing strong electronegativity Ni. Simulations of reaction pathways confirm enhanced catalyzed electrolysis kinetics by the facilitated charge transfer at active O sites around Ni dopants. These findings significantly advance aqueous batteries a step closer toward practical low-cost application.

The zinc‐metal anode (ZMA) is a critical component of rechargeable Zn‐based batteries. Zinc‐dendrite formation on ZMA during cycling causes an internal short‐circuit, thereby limiting long‐term practical operation of batteries. A strategy of introducing zincophilic sites shows promise in suppressing dendrite growth. However, the mechanism is not understood. Here, a detailed study of the mechanism of zincophilic sites based on multiple in situ/ex situ techniques is reported. Using a carbon‐host as a model system with nitrogen sites as zincophilic sites and both ex situ near‐edge X‐ray absorption fine structure (NEXAFS) and in situ Raman spectra, it is shown that zinc ions are bonded with pyridine sites to form ZnN bonds. The ZnN bonds induce spacious nucleation of zinc on carbon‐hosts and suppress zinc‐dendrite formation. The host with zincophilic sites exhibits a homogenous Zn deposition, together with boosted electrochemical performance. This finding underscores the impact of nitrogen zincophilic sites in suppressing zinc‐dendrite formation. It is shown that bonding between zinc ions and zincophilic sites is the mechanism for zincophilic nucleation in the ZMA host. These findings are expected to be of immediate benefit to researchers in battery technologies and materials science.

Engineering high-energy interfacial structures for high-performance electrocatalysis is achieved by chemical coupling of active CoO nanoclusters and high-index facet Mn 3 O 4 nano-octahedrons (hi-Mn 3 O 4 ). At horough characterization, including synchrotron-based near edge X-raya bsorption fine structure,reveals that strong interactions between both components promote the formation of high-energy interfacial Mn-O-Co species and high oxidation state CoO,f rom which electrons are drawn by Mn III -O present in hi-Mn 3 O 4 .The CoO/ hi-Mn 3 O 4 demonstrates an excellent catalytic performance over the conventional metal oxide-based electrocatalysts,which is reflected by 1.2 times higher oxygen evolution reaction (OER) activity than that of Ru/C and ac omparable oxygen reduction reaction (ORR) activity to that of Pt/C as well as ab etter stability than that of Ru/C (95 %v s. 81 %r etained OER activity) and Pt/C (92 %vs. 78 %retained ORR activity after 10 hrunning) in alkaline electrolyte.A proper interfacial structure of heterogeneous catalysts is of great importance because it can promote the catalytic reactions occurring on the surface.[1] High-energy interfacial structures can facilitate adsorption of reactants on the surface of the catalyst, and charge transport, which result in enhancing catalytic performance.[2] Fori nstance,h eterogeneous catalysts composed of Cu and ZnO nanoparticles on Al 2 O 3 supports are effectively used for industrial production of methanol because ahigh-energy interface between Cu, ZnO, and Al 2 O 3 support can enable astrong binding of the reaction intermediates that improves catalytic activity.[3] Thec oordinatively unsaturated ferrous sites are active centers in awide range of catalytic reactions,and their catalytic activity can be significantly enhanced through high-energy interfacial confinement with metal substrates,e .g., Pt, exhibiting efficient carbon monoxide oxidation.[4] Thereby,the rational design of active materials on proper supports to generate high-energy interfacial structures is critical in fabricating high-performance heterogeneous catalysts.Oxygen-involving electrocatalytic reactions such as oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are important energy-relevant conversion processes, [5] which play important roles in metal-air batteries, fuel cells,and water electrolysis.Both OER and ORR involve am ultistep proton-coupled electron transfer, and thus suffer from ak inetically sluggish process.[6] Moreover,s ome technologies such as rechargeable metal-air batteries reversibly involve OER and ORR during the operation, and the use of two different electrocatalysts for OER (e.g.,R u) and ORR (e.g.,Pt) makes these devices much more complex because of combining two different electrodes;a lso,t heir volumetric energy density is unfavorable.[7] Thus,h igh-performance bifunctional oxygen-involving electrocatalysts are highly desirable.Recently,t here is ag reat interest in fabricating nanostructured composite materials by depositing abundan...