Combustion Activation Induced Solid-State Synthesis for N, B Co-Doped Carbon/Zinc Borate Anode with a Boosting of Sodium Storage Performance

Zinc borates have merits of low voltage polarization and suitable redox potential, but usually suffer from low rate capability and poor cycling life, as an emerging anode candidate for Na⁺ storage. Here, a new intercalator-guided synthesis strategy is reported to simultaneously improve rate capability and stabilize cycling life of N, B co-doped carbon/zinc borates (CBZG). The strategy relies on a uniform dispersion of precursors and simultaneously stimulated combustion activation and solid-state reactions capable of scalable preparation. The Na⁺ storage mechanism of CBZG is studied: 1) ex situ XRD and XPS demonstrate two-step reaction sequence of Na⁺ storage: Zn₆ O(OH)(BO₃ )₃ +Na⁺ +e^- ↔3ZnO+Zn₃ B₂ O₆ +NaBO₂ +0.5H₂ ①, Zn₃ B₂ O₆ +6Na⁺ +6e^- ↔3Zn+3Na₂ O+B₂ O₃ ②; reaction ① is irreversible in ether-based electrolyte while reversible in ester-based electrolyte. 2) Electrochemical kinetics reveal that ether-based electrolyte possesses faster Na⁺ storage than ester-based electrolyte. The composite demonstrates an excellent capacity of 437.4 mAh g^-1 in a half-cell, together with application potential in full cells (discharge capacity of 440.1 mAh g^-1 and stable cycle performance of 2000 cycles at 5 A g^-1 ). These studies will undoubtedly provide an avenue for developing novel synthetic methods of carbon-based borates and give new insights into the mechanism of Na⁺ storage in ether-based electrolyte for the desirable sodium storage.

Supramolecular Chiral Nanoarchitectonics

Exploration of molecular functions and material properties based on the control of chirality would be a scientifically elegant approach. Here, the fabrication and function of chiral-featured materials from both chiral and achiral components using a supramolecular nanoarchitectonics concept are discussed. The contents are classified in to three topics: i) chiral nanoarchitectonics of rather general molecular assemblies; ii) chiral nanoarchitectonics of metal-organic frameworks (MOFs); iii) chiral nanoarchitectonics in liquid crystals. MOF structures are based on nanoscopically well-defined coordinations, while mesoscopic orientations of liquid-crystalline phases are often flexibly altered. Discussion on the effects and features in these representative materials systems with totally different natures reveals the universal importance of supramolecular chiral nanoarchitectonics. Amplification of chiral molecular information from molecules to materials-level structures and the creation of chirality from achiral components upon temporal statistic fluctuations are universal, regardless of the nature of the assemblies. These features are thus surely advantageous characteristics for a wide range of applications.

N-Doped C@Zn3 B2 O6 as a Low Cost and Environmentally Friendly Anode Material for Na-Ion Batteries: High Performance and New Reaction Mechanism

Na-ion batteries (NIBs) are ideal candidates for solving the problem of large-scale energy storage, due to the worldwide sodium resource, but the efforts in exploring and synthesizing low-cost and eco-friendly anode materials with convenient technologies and low-cost raw materials are still insufficient. Herein, with the assistance of a simple calcination method and common raw materials, the environmentally friendly and nontoxic N-doped C@Zn₃ B₂ O₆ composite is directly synthesized and proved to be a potential anode material for NIBs. The composite demonstrates a high reversible charge capacity of 446.2 mAh g^-1 and a safe and suitable average voltage of 0.69 V, together with application potential in full cells (discharge capacity of 98.4 mAh g^-1 and long cycle performance of 300 cycles at 1000 mA g^-1 ). In addition, the sodium-ion storage mechanism of N-doped C@Zn₃ B₂ O₆ is subsequently studied through air-insulated ex situ characterizations of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Fourier-transform infrared (FT-IR) spectroscopy, and is found to be rather different from previous reports on borate anode materials for NIBs and lithium-ion batteries. The reaction mechanism is deduced and proposed as: Zn₃ B₂ O₆ + 6Na⁺ + 6e^- ⇋ 3Zn + B₂ O₃ ∙ 3Na₂ O, which indicates that the generated boracic phase is electrochemically active and participates in the later discharge/charge progress.