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Potassium-ion batteries (KIBs) are competitive alternatives to lithium-ion batteries (LIBs) due to the abundant K resources and high energy density. As an indispensable part of the battery, the electrolyte affects the battery capacity, rate capability, cycle life, and safety. Nevertheless, the researches on electrolytes and corresponding solid electrolyte interfaces (SEI) in KIB are still in its infancy and require further attention. In this review, recent progresses of various K+ containing electrolytes for KIBs are summarized comprehensively. Additionally, the effects of salts, solvents, additives, and concentrations on the properties of various electrolyte systems are discussed in detail. Thereafter, interface chemistry between electrode and electrolyte, as well as rational modification strategies for high-performance KIB are reviewed. Finally, the major challenges and the future perspectives are estimated for advanced KIB. This review will provide good directions for the development of high-performance KIB.

Oxygen evolution reaction (OER)-induced reconstruction on precatalysts generally results in surface-reconstructed catalysts with less active species and thus low mass activity. Herein, the deeply r...

The calcium-ion battery is an emerging energy storage system that has attracted considerable attention recently. However, the absence of high-performance cathode materials is one of the main challe...

N-doped carbon-confined transition metal nanocatalysts display efficient oxygen reduction reaction (ORR) performance comparable to commercial Pt/C electrocatalysts because of their efficient charge transfer from metal atoms to active N sites. However, the sheathed active sites inside the electrocatalysts and relatively large-size confined metal particles greatly restrict their activity improvement. Here, we develop a facile and efficient "MOFs plus ZIFs" synthesis strategy to successfully construct ultrafine sub-5 nm Co nanodots confined into superficial N-doped carbon nanowires (Co@C@NC) via a well-designed synthesis process. The unique synthesis mechanism is based on low-pressure vapor superassembly of thin zeolitic imidazolate framework (ZIF) coatings on metal-organic framework substrates. During the successive pyrolysis, the preferential formation of the robust N-doped carbon shell from the ZIF-67 shell keeps the core morphology without shrinkage and limits the growth of Co nanodots. Benefiting from this architecture with accessible and rich active N sites on the surface, stable carbon confined architecture, and large surface area, the Co@C@NC exhibits excellent ORR performance, catching up to commercial Pt/C. Density functional theory demonstrates that the confined Co nanodots efficiently enhance the charge density of superficial active N sites by interfacial charge transfer, thus accelerating the ORR process.

Unique interfacial properties within heterostructures play vital roles in enhancing hydrogen evolution reaction (HER) electrocatalysis. On the basis of the MoO2-Ni heterostructure, we hereby propos...

Two-dimensional (2D) nanostructure engineering and surface modification with functional groups are of great importance to anode materials for rechargeable lithium-ion batteries. Herein, stacked NiO nanosheets@carbon (denoted as NiO@C) and 3 nm-ultrathin NiO nanosheets@functionalized carbon with surface functional groups NO3-, CO32-, OH-, and COOH- (denoted as NiO@FC) were prepared via a facile one-pot reaction and topotactic conversion. Specifically, NiO@FC exhibits excellent lithium storage performance: the capacity of NiO@FC is 489.2 mA h g-1, higher than that of NiO@C (1018.7 mA h g-1 at 0.2 A g-1), and maintains a capacity of 1133 mA h g-1 after 800 cycles, which exceed that of all previously reported NiO anodes. The enhanced lithium storage performance is attributed to the sufficient void space, which offers buffer space for volume change and speeds up the diffusion of Li+ ions. In addition, the surface functional groups were proved to not only hinder the agglomeration of nanosheets but also further donate active sites and improve storage capacity. These advantageous features achieved by designing such a stacked structure with functionalized carbon modification provide a promising strategy for the preparation of high-performance anode materials and other 2D functional materials.

Realizing stable cycling performance with high areal capacity is a great challenge for metal-ion battery anodes. Achieveing high areal capacity generally requires the electrode in a high active loading with increased electrode thickness, which is not beneficial to the cycling stability. In this work, novel nanosheet-assembled compact CaV4O9 microflowers are firstly synthesized through a facile method, which exhibit both high areal capacity and stable cycling performance at high mass loadings. The compact microflower structure leads to an increased tap density of the electrode materials, benefiting to reduce the anode thickness at high mass loadings. Meanwhile, the assembled nanosheets maintain the nano-effects of the active materials for favorable electrochemical reactions. These merits together with the intrinsic superior electrochemical properties of CaV4O9, result in the outstanding electrochemical performance. When used as Li-ion battery anodes, a high areal capcity of ~2.5 mAh cm−2 at a high mass loading of 4.4 mg cm−2 is obtained, and a stable cycling over 400 cycles with the areal capacity over 1.5 mAh cm−2 is demonstrated. Besides, the superior electrochemical performance at high mass loadings is also observed for Na storage. These achievements may pave the way for constructing applicable high-capacity and stable anode materials in metal-ion batteries.

Metal oxides are considered as attractive candidates as anode materials for lithium ion batteries (LIBs) due to their high capacities compared to commercialized graphite. However, fast capacity fading, which is caused by inherent large volume expansions and agglomeration of active particles upon cycling, is a great challenge. Herein, we propose the design of porous CaFe2O4 electrode material to address the above issue. Compared to pristine iron oxides, CaFe2O4 exhibits a distinct trade-off in terms of high capacity and long-term stability, which is beneficial to the potential practical applications. Such a trade-off effect is attributed to the synergistic effect between the porous structure and the in situ formed CaO nanograins during charging/discharging processes. This work provides an effective strategy in achieving anode materials with high capacity and long-term stability for next-generation LIBs.

Transition metal phosphides or partially phosphatized oxides usually suffer from surface reconstruction during oxygen evolution reaction (OER), but still possess enhanced catalytic activity than directly synthesized oxides, which has aroused great interest in exploring the causes of such high catalytic activity. To monitor electronic property of catalyst during the OER can provide crucial insights into catalytic ability. Here we design a planar electrochemical microdevice based on individual thin-film catalyst, and for the first time explore the continuous electric conductance evolution of lattice P-doped oxides during the electrochemical activation process. Moreover, combining on-chip electrochemical impedance spectra measurements, in situ I-V measurements, and theoretical simulations of reconstructed lattice P-doped oxides, the effect of P–O groups on new-formed oxides is clarified. The induced electronic coupling between new-formed oxides and P-O groups has been studied and demonstrated. The coupled P–O groups effectively promote the metal–oxygen covalency of new-formed oxides, which accelerates electron transfer between active metallic center and oxygen adsorbates, thus leading to the enhanced electrocatalytic activity. Our study highlights the role of surface P–O groups in Co3O4 during the OER, and such unique on-chip electrochemical microdevice platform can also be applied in other related fields to understand the dynamic behavior of energy materials at nanoscale.

Evaluating the alkaline water electrolysis (AWE) at 50-80 °C required in industry can veritably promote practical applications. Here, the thermally induced complete reconstruction (TICR) of molybdate oxygen evolution reaction (OER) pre-catalysts at 51.9 °C and its fundamental mechanism are uncovered. The dynamic reconstruction processes, the real active species, and stereoscopic structural characteristics are identified by in situ low-/high-temperature Raman, ex situ microscopy, and electron tomography. The completely reconstructed (CR) catalyst (denoted as cat.-51.9) is interconnected by thermodynamically stable (oxy)hydroxide nanoparticles, with abundant boundaries and low crystallinity. For alkaline OER, cat.-51.9 exhibits a low overpotential (282.3 mV at 20 mA cm-2 , 25.0 °C) and ultrastable catalysis at 51.9 °C (250 h, with a negligible activity decay of 19.6 µV h-1 ). The experimental observations combined with theoretical analyses confirm the fast catalytic kinetics enabled by the co-effect of boundaries and vacancies. The coupled cat.-51.9 and MoO2 -Ni hydrogen-evolving arrays provide stable electrolysis operation at 51.9 °C for 220 h. This work uncovers new reconstruction phenomenon of pre-catalysts under realistic conditions and exceptional durability of CR catalysts toward practical high-temperature AWE.

High-capacity anodes of lithium-ion batteries generally suffer from poor electrical conductivity, large volume variation, and low tap density caused by prepared nanostructures, which make it an obstacle to achieve both high-areal capacity and stable cycling performance for practical applications. Herein, micrometer-sized porous Fe2 N/C bulk is prepared to tackle the aforementioned issues, and thus realize both high-areal capacity and stable cycling performance at high mass loading. The porous structure in Fe2 N/C bulk is beneficial to alleviate the volumetric change. In addition, the N-doped carbon conducting networks with high electrical conductivity provide a fast charge transfer pathway. Meanwhile, the micrometer-sized Fe2 N/C bulk exhibits a higher tap density than that of commercial graphite powder (1.03 g cm-3 ), which facilitates the preparation of thinner electrode at high mass loadings. As a result, a high-areal capacity of above 4.2 mA h cm-2 at 0.45 mA cm-2 is obtained at a high mass loading of 7.0 mg cm-2 for LIBs, which still maintains at 2.59 mA h cm-2 after 200 cycles with a capacity retention of 98.8% at 0.89 mA cm-2 .