Potassium-ion batteries (KIBs) are new-concept of low-cost secondary batteries, but the sluggish kinetics and huge volume expansion during cycling, both rooted in the size of large K ions, lead to poor electrochemical behavior. Here, a bamboo-like MoS 2 /N-doped-C hollow tubes are presented with an expanded interlayer distance of 10 Å as a high-capacity and stable anode material for KIBs. The bamboo-like structure provides gaps along axial direction in addition to inner cylinder hollow space to mitigate the strains in both radial and vertical directions that ultimately leads to a high structural integrity for stable long-term cycling. Apart from being a constituent of the interstratified structure the N-doped-C layers weave a cage to hold the potassiation products (polysulfide and the Mo nanoparticles) together, thereby effectively hindering the continuing growth of solid electrolyte interphase in the interior of particles. The density functional theory calculations prove that the MoS 2 /N-doped-C atomic interface can provide an additional attraction toward potassium ion. As a result, it delivers a high capacity at a low current density (330 mAh g −1 at 50 mA g −1 after 50 cycles) and a high-capacity retention at a high current density (151 mAh g −1 at 500 mA g −1 after 1000 cycles).

No abstract

Potassium-ion batteries are potential alternatives to lithium-ion batteries for large-scale energy storage considering the low cost and high abundance of potassium. However, it is challenging to obtain stable electrode materials capable of undergoing long-term potassiation/depotassiation due to the high accumulated stress associated with the huge volume variation of the electrode. Here, we simulate the von Mises stress distributions of four different carbon three-dimensional models under an isotropic initial stress by the finite element method and reveal the critical role of the structure of a hollow multihole bowl on the strain−relaxation behavior. In this regard, nitrogen/oxygen codoped carbon hollow multihole bowls (CHMBs) are synthesized via hydrothermal carbonization coupled with an emulsiontemplating strategy using biomass as the carbon source. Consistent with our simulation results, the CHMB anode remains stable for over 1000 cycles and delivers a high reversible capacity of 304 mAh g −1 at 0.1 A g −1 . In addition to the reduced stress accumulation, the good electrochemical performances are also attributed to the surface capacitive mechanism and the shortened electron/ion transport distance in CHMBs. In particular, the CHMB composite electrode has a volumetric specific capacity 56% higher than that of hollow spheres due to the high tapped density of the bowl-shaped particles.

Figure 7. a) Schematic figures showing the procedure of in situ hydrolysis and interaction mechanisms among PEO chains and SiO 2 . b) Arrhenius plots of ionic conductivity of ceramic-free SPE, PEO-fumed SiO 2 CPE, ex situ CPE, and in situ CPE. a,b) Reproduced with permission. [69] Copyright 2015, American Chemical Society. c) Schematic illustration for the synthesis of ceramic nanowire-filled CPEs, together with SEM images for the CPEs with 15 wt% nanowire fillers. Reproduced with permission. [74] Copyright 2015, American Chemical Society. d) Comparison of possible Li-ion conduction pathways in CPEs with nanoparticles, random nanowires and aligned nanowires. Reproduced with permission. [75] Copyright 2017, Springer Nature. e) Schematic of the CPEs with the interwelded garnet nanofiber network. Reproduced with permission. [78] Copyright 2017, The Authors, published by National Academy of Sciences. f) Schematic showing the synthetic process of the SiO 2 -aerogel-reinforced CPE. Reproduced with permission. [80] Copyright 2018, Wiley-VCH.

COMMUNICATION (1 of 7)2D material is an excellent starting point for developing catalysts, size-selective membranes, and electronics and energy storage devices because of its atomic thickness and "nano-effect." [1] However, pores that serve as tunnels for target species are often preferred and need to be introduced in some cases. Graphene itself is an example as it is not permeable to gas species, metal ions, and liquid molecules. In order to realize their successful application in molecular sieves and energy storage, recently new graphene nanomesh and holey graphene are created to achieve excellent transport across the plane and ultimate access to the inner surfaces. [2] The common hole-making methods are postprocessing of graphene, such as ultraviolet-induced oxidative etching and lithography. [2c,d] The general chemical/mechanical exfoliation method for graphene is not applicable to synthesize porous graphene because high-crystalline peelable porous graphite cannot be produced.2D layered double hydroxide (LDH) is another important member of the 2D material family and has shown exciting perspectives in many fields, especially in electrocatalysis (e.g., the hydrogen and oxygen evolution reactions (HER and OER) in water splitting). [3] However, as opposed to graphene, the 2D hydroxide with in-plane pores has rarely been reported so far. If the common chemical-exfoliation strategy of 2D metal hydroxide were to be applied to synthesize holey 2D hydroxide, getting high-quality porous single-crystalline precursor would be the crucial prerequisite because most porous materials are amorphous or polycrystalline. [4] Fortunately, recently we have developed mesoporous single-crystalline Co(OH) 2 nanoplates via a copolymer-templating technique, which makes the synthesis of holey hydroxide 2D material possible. [5] OER is the oxidative half reaction of water splitting that involves the transfer of four protons and four electrons. [3d,6] Therefore, it is kinetically sluggish and always requires conspicuous overpotential. [3d,6,7] The precious-metal catalysts, e.g., IrO 2 and RuO 2 , despite performing well on the catalysis toward OER, are extremely scarce on the earth and also expensive, so earth-abundant transition-metal electrocatalysts including oxides/hydroxides and their derivatives have been developed recently. [8] Especially, some reports pointed that transition-metal LDH can be exfoliated into 2D nanosheets with large anisotropy to get extraordinarily improved catalytic performances, because Creating nanosized pores in 2D materials can increase the edge sites, improve the mass transfer, and contribute to different physical properties, which shows potential applications in many fields including filtration membranes, electronics and energy storage devices, and catalysts. An iconic member of this type of material is porous graphene. Herein, a unique 2D layered double hydroxide (LDH) nanomesh is designed and synthesized as a new class of 2D holey materials. It represents the first case of exfoliation method for p...