No abstract

Silicon (Si) has been recognized as a promising alternative to graphite anode materials for advanced lithium-ion batteries (LIBs) owing to its superior theoretical capacity and low discharge voltage. However, Si-based anodes undergo structural pulverization during cycling due to the large volume expansion (ca. 300–400%) and continuous formation of an unstable solid electrolyte interphase (SEI), resulting in fast capacity fading. To address this challenge, a series of different amounts of silicon nanoparticles (Si NPs)-encapsulated hollow porous N-doped/Co-incorporated carbon nanocubes (denoted as p-CoNC@SiX, where X = 50, 80, and 100) as anode materials for LIBs are reported in this paper. These hollow nanocubic materials were derived by facile annealing of different contents of Si NPs-encapsulated Zn/Co-bimetallic zeolitic imidazolate frameworks (ZIF@Si) as self-sacrificial templates. Owing to the advantages of well-defined hollow framework clusters and highly conductive hollow carbon frameworks, the hollow porous p-CoNC@SiX significantly improved the electronic conductivity and Li+ diffusion coefficient by an order of magnitude higher than that of Si NPs. The as-prepared p-CoNC@Si80 with 80 wt % Si NPs delivered a continuously increasing specific capacity of 1008 mAh g–1 at 500 mA g–1 over 500 cycles, excellent reversible capacity (∼1361 mAh g–1 at 0.1 A g–1), and superior rate capability (∼603 mAh g–1 at 3 A g–1) along with an unprecedented long-life cyclic stability of ∼1218 mAh g–1 at 1 A g–1 over 1000 cycles caused by low volume expansion (9.92%) and suppressed SEI side reactions. These findings provide new insights into the development of highly reversible Si-based anode materials for advanced LIBs.

Graphitic carbon nitride (g–C3N4) is widely used in organic metal‐ion batteries owing to its high porosity, facile synthesis, stability, and high‐rate performance. However, pristine g–C3N4 nanosheets exhibit poor electrical conductivity, irreversible metal‐ion storage capacity, and short‐term cycling owing to their high concentration of graphitic–N species. Herein, a series of 3,4:9,10‐perylenetetracarboxylic diimide‐coupled g–C3N4 composite anode materials, CN–PIx (x = 0.2, 0.5, 0.75, and 1), was investigated, which exhibited an unusually high surface nitrogen content (23.19–39.92 at.%) and the highest pyridinic–N, pyrrolic–N, and graphitic–N contents reported to date. The CN–PI1 anode delivers an unprecedented and continuously increasing ultrahigh discharging capacity of exceeding 8400 mAh g−1 (1.96 mWh cm−2) at 100 mA g−1 with high specific energy density (Esp) of ∼7700 Wh kg−1 and the volumetric energy density (Ev) of ∼14956 Wh L−1 and an excellent long‐term stability (414 mAh g−1 or 0.579 mWh cm−2 at 1 A g−1). Furthermore, the activation of the CN–PIx electrodes contributes to their superior electrochemical performance, resulting from the fact that the Li+ is not only stored in the CN–PIx composites but also CN–PIx activated the Li0 adlayer on the CN–PI1–Cu heterojunction as an SEI layer to avoid the direct contact of Li0 phase and the electrolyte. The CN–PI1 full cell with LiCoO2 as the cathode delivers a discharge capacity of ∼587 mAh g−1 at a 1 A g−1 after 250 cycles with a Coulombic efficiency nearly 99%. This study provides a strategy to develop N‐doped g–C3N4‐based anode materials for realizing long‐lasting energy storage devices.

Finding high-performance, low-cost, efficient catalysts for oxygen reduction reactions (ORR) is essential for sustainable energy conversion systems. Herein, highly efficient and durable iron (Fe) and cobalt (Co)-supported nitrogen (N) and sulfur (S) codoped three-dimensional carbon nanofibers (FeCoÀ N, S@CNFs) were synthesized via electrospinning followed by carbonization. The as-prepared FeCoÀ N,S@CNFs served as efficient ORR catalysts in alkaline 0.1 m KOH solutions that were N 2 and O 2saturated.The experimental results revealed that FeCoÀ N,S@CNFs were highly active ORR catalysts with defectrich active pyridinic N and pyrrolic N and metal bonds to N and S atom sites, which enhanced the ORR activity. FeCoÀ N,S@CNFs exhibited a high onset potential (E onset = 0.89 V) and half-wave potential (E 1/2 = 0.85 V), similar to the electrocatalytic activity of commercial Pt/C. Additionally, the durability of the as-prepared FeCoÀ N,S@CNFs catalysts was maintained for 14 h with longterm stability and high tolerance to methanol stability, accounting for their excellent catalytic ability. Furthermore, CoÀ N@CNFs, FeÀ N@CNFs, and varying Fe and Co ratios were compared with those of FeCoÀ