Synergistically Assembled Li2S/FWNTs@Reduced Graphene Oxide Nanobundle Forest for Free‐Standing High‐Performance Li2S Cathodes

Lithium sulfide (Li₂S) has attracted increasing attention as a promising cathode because of its compatibility with more practical lithium‐free anode materials and its high specific capacity. However, it is still a challenge to develop Li₂S cathodes with low electrochemical overpotential, high capacity and reversibility, and good rate performance. This work designs and fabricates a practical Li₂S cathode composed of Li₂S/few‐walled carbon nanotubes@reduced graphene oxide nanobundle forest (Li₂S/FWNTs@rGO NBF). Hierarchical nanostructures are obtained by annealing the Li₂SO₄/FWNTs@GO NBF, which is prepared by a facile and scalable solution‐based self‐assembly method. Systematic characterizations reveal that in this unique NBF nanostructure, FWNTs act as axial shafts to direct the structure, Li₂S serves as the internal active material, and GO sheets provide an external coating to minimize the direct contact of Li₂S with the electrolyte. When used as a cathode, the Li₂S/FWNTs@rGO NBF achieve a high capacity of 868 mAh g^?1_Li2S at 0.2C after 300 cycles and an outstanding rate performance of 433 mAh g^?1_Li2S even at 10C, suggesting that this Li₂S cathode is a promising candidate for ultrafast charge/discharge applications. The design and synthetic strategies outlined here can be readily applied to the processing of other novel functional materials to obtain a much wider range of applications.     

An Abnormal 3.7 Volt O3‐Type Sodium‐Ion Battery Cathode

Layered O3‐type sodium oxides (NaMO₂, M=transition metal) commonly exhibit an O3–P3 phase transition, which occurs at a low redox voltage of about 3 V (vs. Na⁺/Na) during sodium extraction and insertion, with the result that almost 50 % of their total capacity lies at this low voltage region, and they possess insufficient energy density as cathode materials for sodium‐ion batteries (NIBs). Therefore, development of high‐voltage O3‐type cathodes remains challenging because it is difficult to raise the phase‐transition voltage by reasonable structure modulation. A new example of O3‐type sodium insertion materials is presented for use in NIBs. The designed O3‐type Na_0.7Ni_0.35Sn_0.65O₂ material displays a highest redox potential of 3.7 V (vs. Na⁺/Na) among the reported O3‐type materials based on the Ni²⁺/Ni³⁺ couple, by virtue of its increased Ni?O bond ionicity through reduced orbital overlap between transition metals and oxygen within the MO₂ slabs. This study provides an orbital‐level understanding of the operating potentials of the nominal redox couples for O3‐NaMO₂ cathodes. The strategy described could be used to tailor electrodes for improved performance.     

Thermal Reductive Perforation of Graphene Cathode for High-Performance Aluminum-Ion Batteries

Controlling the structure of graphene-based materials with improved ion intercalation and diffusivity is crucial for their applications, such as in aluminum-ion batteries (AIBs). Due to the large size of AlCl₄⁻ ions, graphene-based cathodes have specific capacities of ≈60 to 148 mAh g⁻¹, limiting the development of AIBs. A thermal reductive perforation (TRP) strategy is presented, which converts three-layer graphene nanosheets to surface-perforated graphene materials under mild temperature (400 °C). The thermal decomposition of block copolymers used in the TRP process generates active radicals to deplete oxygen and create graphene fragments. The resultant material has a three-layer feature, in-plane nanopores, >50% expanded interlayer spacing, and a low oxygen content comparable to graphene annealed at a high temperature of ≈3000 °C. When applied as an AIB cathode, it delivers a reversible capacity of 197 mAh g⁻¹ at a current density of 2 A g⁻¹ and reaches 92.5% of the theoretical capacity predicted by density-functional theory simulations.     

Enhancing Oxygen Reduction Activity and Cr Tolerance of Solid Oxide Fuel Cell Cathodes by a Multiphase Catalyst Coating

Intermediate temperature solid oxide fuel cells (IT-SOFCs) are cost-effective and efficient energy conversion systems. The sluggish oxygen reduction reaction (ORR) and the degradation of cathodes are critical challenges to the commercialization of IT-SOFCs. Here, a highly efficient multiphase (MP) catalyst coating, consisting of Ba_1−xCo_0.7Fe_0.2Nb_0.1O_3−δ (BCFN) and BaCO₃, to enhance the ORR activity and durability of the state-of-the-art lanthanum strontium cobalt ferrite (La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ, LSCF) cathode is reported. The conformal MP catalyst-coated LSCF cathode shows a polarization resistance (R_p) of 0.048 Ω cm² at 650 °C, about one order of magnitude smaller than that of the bare LSCF. In an accelerated Cr-poisoning test, the degradation rate of the catalyst-coated LSCF electrode is 10⁻³ Ω cm² h⁻¹ (0.59% h⁻¹) over 200 h, only one fifth of the degradation rate of the bare LSCF electrode at 750 °C. In addition, anode-supported single cells with the MP catalyst-coated LSCF cathode show a dramatically enhanced peak power density (1.4 W cm⁻² vs 0.67 W cm⁻² at 750 °C) and increased durability against Cr and H₂O. Both experimental results and density functional theory-based calculations indicate that the BCFN phase improves the ORR activity while the BaCO₃ phase enhances the stability of the LSCF cathode.     

An Ultrastable Aqueous Iodine-Hydrogen Gas Battery

Rechargeable hydrogen gas batteries are highly desirable for large-scale energy storage because of their long life cycle, high round trip efficiency, fast reaction kinetics, and hydrogen gas profusion. Coupling advanced cathode chemistries with hydrogen gas anode is an emerging and exciting area of research. Here, a novel high-performance aqueous iodine-hydrogen gas (I₂-H₂) battery using iodine as cathode and hydrogen gas as the electrocatalytic anode in environmentally benign aqueous electrolytes is reported. The working chemistry of the battery involves I₂/I⁻ solid-liquid reactions occurring over the cathode along with H₂/H₂O gas-liquid reactions at the anode, achieving a high rate performance of 100 C and long-lasting stability of over 60 000 cycles. Additionally, the static aqueous I₂-H₂ battery displays a volumetric capacity of 15.5 Ah L⁻¹ along with good self-healing capability towards cell overcharge. The current battery design exhibits robust electrochemical performance irrespective of acidic, neutral, and alkaline electrolyte systems. This study paves the way towards the industrialization of economically effective, high-power density, and long-term I₂-H₂ batteries for large-scale energy storage applications.     

Ultrafast Rechargeable Aqueous Zinc-Ion Batteries Based on Stable Radical Chemistry

Aqueous zinc-ion batteries (ZIBs) are a promising candidate for fast-charging energy-storage systems due to its attractive ionic conductivity of water-based electrolyte, high theoretical energy density, and low cost. Current strategies toward high-rate ZIBs mainly focus on the improvement of ionic or electron conductivity within cathodes. However, enhancing intrinsic electrochemical reaction kinetics of active materials to achieve fast Zn²⁺ storage has been greatly omitted. Herein, for the first time, stable radical intermediate generation is demonstrated in a typical organic electrode material (methylene blue [MB]), which effectively decreases the reaction energy barrier and enhances the intrinsic kinetics of MB cathode, enabling ultrafast Zn²⁺ storage. Meanwhile, anionic co-intercalation essentially avoids MB molecules rearranging their configuration and sharing Zn²⁺ with adjacent functional groups, thus keeps the structure stable. As a result, Zn–MB batteries exhibit an excellent rate capability up to 500C and ultralong life of 20 000 cycles with a negligible 0.07% capacity decay per cycle at 100C, which is superior to that of most reported aqueous ZIBs batteries. This work provides a novel strategy of stable radical chemistry for ultrafast-charging aqueous ZIBs, which can be introduced to other appropriate organic materials and multivalent ion battery systems.     

Wide Working Temperature Range Rechargeable Lithium–Sulfur Batteries: A Critical Review

At the technological forefront of energy storage, there is still a continuous upsurge in demand for high energy and power density batteries that can operate at a wide range of temperature. Rechargeable lithium sulfur batteries stand out among other advanced cell concepts owing to their ultrahigh theoretical gravimetric energy density characteristic as well as merits of low cost and environmental friendliness. Although achieving good operability of ambient lithium sulfur batteries, extending their workability to both higher and lower temperatures is also of paramount importance especially for future task-specific applications. As a first attempt, this review presents a comprehensive understanding on the advances, challenges, and future research directions on lithium sulfur batteries operating at both low and high temperature extremes. From a material perspective, the workability of sulfur-containing cathode materials, advanced electrolytes (from conventional liquid to quasi- and all-solid-state electrolytes), lithium metal anodes and the electrochemically inert components (separators and interlayer materials) at extreme temperatures are thoroughly analyzed. The insurmountable challenges and mechanistic understandings caused by thermal changes are critically reviewed. Finally, potential future research directions and prospects for lithium sulfur batteries operated at a wide range of temperature are also proposed.     

Optimized Cathode for High-Energy Sodium-Ion Based Dual-Ion Full Battery with Fast Kinetics

The most used systems based on the graphite-based cathode show unsatisfactory performance in dual-ion batteries. Developing new type cathode materials with high capacity for new type anions storage is an effective way to improve the total performance of dual-ion batteries. Herein, a protonated polyaniline (P-PANI) cathode is prepared to realize efficient and stable storage of ClO₄^–, and a high reversible capacity of 143 mAh g⁻¹ at 0.2 A g⁻¹ after 200 cycles can be obtained, which is competitive compared with common graphite cathodes. In addition, the highly reversible coordination storage mechanism between ClO₄⁻ and P-PANI cathode is indicated, rather than the labored intercalation reactions between PF₆⁻ and graphite. Subsequently, a full cell (P-PANI//N-PDHC) fabricated with a P-PANI cathode and hard carbon anode (N-PDHC) can deliver a high energy density of 284 Wh kg^–1 for 2000 cycles at 2 A g^–1, and the relevant pouch-type full cell can easily power a smartphone. In general, this work may promote the exploitation of sodium-based dual-ion batteries in practical application.     

Hydrogenated V2O5 Nanosheets for Superior Lithium Storage Properties

V₂O₅ is a promising cathode material for lithium ion batteries boasting a large energy density due to its high capacity as well as abundant source and low cost. However, the poor chemical diffusion of Li⁺, low conductivity, and poor cycling stability limit its practical application. Herein, oxygen‐deficient V₂O₅ nanosheets prepared by hydrogenation at 200 °C with superior lithium storage properties are described. The hydrogenated V₂O₅ (H‐V₂O₅) nanosheets deliver an initial discharge capacity as high as 259 mAh g^?1 and it remains 55% when the current density is increased 20 times from 0.1 to 2 A g^?1. The H‐V₂O₅ electrode has excellent cycling stability with only 0.05% capacity decay per cycle after stabilization. The effects of oxygen defects mainly at bridging O(II) sites on Li⁺ diffusion and overall electrochemical lithium storage performance are revealed. The results reveal here a simple and effective strategy to improve the capacity, rate capability, and cycling stability of V₂O₅ materials which have large potential in energy storage and conversion applications.     

Lithium–Iron Fluoride Battery with In Situ Surface Protection

Lithium–metal fluoride (MF) batteries offer the highest theoretical energy density, exceeding that of the sulfur–lithium cells. However, conversion‐type MF cathodes suffer from high resistance, small capacity utilization at room temperature, irreversible structural changes, and rapid capacity fading with cycling. In this study, the successful application of the approach to overcome such limitations and dramatically enhance electrochemical performance of Li–MF cells is reported. By using iron fluoride (FeF₂) as an example, Li–MF cells capable of achieving near‐theoretical capacity utilization are shown when MF is infiltrated into the carbon mesopores. Most importantly, the ability of electrolytes based on the lithium bis(fluorosulfonyl)imide (LiFSI) salt is presented to successfully prevent the cathode dissolution and leaching via in situ formation of a Li ion permeable protective surface layer. This layer forms as a result of electrolyte reduction/oxidation reactions during the first cycle of the conversion reaction, thus minimizing the capacity losses during cycling. Postmortem analysis shows the absence of Li dendrites, which is important for safer use of Li metal anodes. As a result, Li–FeF₂ cells demonstrate over 1000 stable cycles. Quantum chemistry calculations and postmortem analysis provide insights into the mechanisms of the passivation layer formation and the performance boost.