shuttle effect of polysulfide. [3] The suppression of the polysulfide shuttle effect is the primary challenge that has hindered the development of lithium-sulfur batteries. The ideal sulfur cathode host should have: (i) a highly porous structure with interconnected architecture to encapsulate sulfur, (ii) strong capability to restrain soluble polysulfides, (iii) high electronic conductivity, and (iv) flexible but robust mechanical properties.Carbon materials with well-designed pore structures, such as mesoporous carbon [4] and carbon nanotubes, [5] have been utilized to restrain the migration of soluble polysulfides from the cathode. Carbon materials can effectively improve the electronic conductivity of sulfur cathodes, and the as-fabricated lithium-sulfur cells showed high specific capacities during the initial few cycles. However, there has been a serious decay of capacity during long-term cycling. It is mainly ascribed to the weak intrinsic interactions between nonpolar carbon and polar polysulfides intermediate, and the large volume expansion/extraction of sulfur compounds during the discharge/ charge processes. [6] The physical barriers provided by sequestration and adsorption in carbon materials can only slow down diffusion of lithium polysulfides out of cathodes in the shortto medium-term of cycling (<100 cycles). Additionally, weak interaction can cause the detachment and separation of lithium sulfides (Li 2 S x , 1 < x < 2, the fully discharged products), from carbon matrix, which will induce irreversible active mass loss and isolation of electrical contacts. Therefore, strong physical and chemical interactions between sulfur/lithium polysulfides and the host materials are crucial to suppress polysulfides shuttling effects and capacity decay. It has been discovered that surface functionalized host materials, such as reduced graphene oxides, [1] polar metal oxides (MnO 2 , [7] Ti 4 O 7[8] ), metal-organic frameworks (MOFs), [9] and metal carbide MXene, [10] showed much better properties because of their hydrophilic surfaces that can bind lithium polysulfides via polar-polar interactions.Recently, a large family of ternary metal carbides, nitrides, or carbonitrides has been successfully prepared. These are termed as "MXene" and are denoted as M n + 1 X n T x , where M is an transition metal such as Ti or V, X is C and/or N, and T is a surface termination group (e.g., O, OH, and F). [11] They have been emerged as brand-new 2D materials with potential applications as electrode materials. Owing to layered structure, high electronic conductivity, remarkable chemical durability, Crumpled nitrogen-doped MXene nanosheets with strong physical and chemical coadsorption of polysulfides are synthesized by a novel one-step approach and then utilized as a new sulfur host for lithium-sulfur batteries. The nitrogendoping strategy enables introduction of heteroatoms into MXene nanosheets and simultaneously induces a well-defined porous structure, high surface area, and large pore volume. The as-prepared nitrogen-dope...
HIGHLIGHTSNovel synthesis of aerogel-like porous MXene architectures Porous MXene architectures can effectively prevent the restack of MXene nanosheets Porous MXene demonstrated a high electroadsorption capacity MXene electrodes achieved a high capacitive deionization capacity
Two-dimensional Si nanosheets have been studied as a promising candidate for lithium-ion battery anode materials. However, Si nanosheets reported so far showed poor cycling performances and required further improvements. In this work, we utilize inexpensive natural clays for preparing high quality Si nanosheets via a one-step simultaneous molten salt-induced exfoliation and chemical reduction process. This approach produces high purity mesoporous Si nanosheets in high yield. As a control experiment, two-step process (pre-exfoliated silicate sheets and subsequent chemical reduction) cannot sustain their original two-dimensional structure. In contrast, one-step method results in a production of 5 nm-thick highly porous Si nanosheets. Carbon-coated Si nanosheet anodes exhibit a high reversible capacity of 865 mAh g(-1) at 1.0 A g(-1) with an outstanding capacity retention of 92.3% after 500 cycles. It also delivers high rate capability, corresponding to a capacity of 60% at 20 A g(-1) compared to that of 2.0 A g(-1). Furthermore, the Si nanosheet electrodes show volume expansion of only 42% after 200 cycles.
Forthcoming flexible/wearable electronic devices with shape diversity and mobile usability garner a great deal of attention as an innovative technology to bring unprecedented changes in our daily lives. From the power source point of view, conventional rechargeable batteries (one representative example is a lithium-ion battery) with fixed shapes and sizes have intrinsic limitations in fulfilling design/performance requirements for the flexible/wearable electronics. Here, as a facile and efficient strategy to address this formidable challenge, we demonstrate a new class of printable solid-state batteries (referred to as "PRISS batteries"). Through simple stencil printing process (followed by ultraviolet (UV) cross-linking), solid-state composite electrolyte (SCE) layer and SCE matrix-embedded electrodes are consecutively printed on arbitrary objects of complex geometries, eventually leading to fully integrated, multilayer-structured PRISS batteries with various form factors far beyond those achievable by conventional battery technologies. Tuning rheological properties of SCE paste and electrode slurry toward thixotropic fluid characteristics, along with well-tailored core elements including UV-cured triacrylate polymer and high boiling point electrolyte, is a key-enabling technology for the realization of PRISS batteries. This process/material uniqueness allows us to remove extra processing steps (related to solvent drying and liquid-electrolyte injection) and also conventional microporous separator membranes, thereupon enabling the seamless integration of shape-conformable PRISS batteries (including letters-shaped ones) into complex-shaped objects. Electrochemical behavior of PRISS batteries is elucidated via an in-depth analysis of cell impedance, which provides a theoretical basis to enable sustainable improvement of cell performance. We envision that PRISS batteries hold great promise as a reliable and scalable platform technology to open a new concept of cell architecture and fabrication route toward flexible power sources with exceptional shape conformability and aesthetic versatility.
In article number https://doi.org/10.1002/aenm.201702485 Dan Wang and Guoxiu Wang and co‐workers design a novel strategy for doping heteroatomic nitrogen into MXene frameworks. The resultant nitrogen‐doped MXene nanosheets demonstrate a well‐defined porous structure, a high surface area and large pore volume. The nitrogen‐doped porous MXene nanosheets are successfully used for strong physical and chemical co‐absorption of polysulfides. Lithium‐sulfur batteries, based on porous N‐doped MXene nanosheets/sulfur composites, exhibit an outstanding electrochemical performance.
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