TiC/C core/shell nanowires arrays as advanced anode of sodium ion batteries

Design and Synthesis Strategy of MXenes-Based Anode Materials for Sodium-Ion Batteries and Progress of First-Principles Research

MXenes-based materials are considered to be one of the most promising electrode materials in the field of sodium-ion batteries due to their excellent flexibility, high conductivity and tuneable surface functional groups. However, MXenes often have severe self-agglomeration, low capacity and unsatisfactory durability, which affects their practical value. The design and synthesis of advanced heterostructures with advanced chemical structures and excellent electrochemical performance for sodium-ion batteries have been widely studied and developed in the field of energy storage devices. In this review, the design and synthesis strategies of MXenes-based sodium-ion battery anode materials and the influence of various synthesis strategies on the structure and properties of MXenes-based materials are comprehensively summarized. Then, the first-principles research progress of MXenes-based sodium-ion battery anode materials is summarized, and the relationship between the storage mechanism and structure of sodium-ion batteries and the electrochemical performance is revealed. Finally, the key challenges and future research directions of the current design and synthesis strategies and first principles of these MXenes-based sodium-ion battery anode materials are introduced.

Hierarchical hollow superstructure cobalt selenide bird nests for high-performance lithium storage

The inferior cycling performance caused by large volume variation is the main problem that restricts the application of cobalt selenides in lithium-ion batteries. Herein, we synthesize raspberry-like Co-ethylene glycol precursor. It is further selenized into the hierarchical hollow superstructure CoSe₂/CoSe bird nests that are assembled by the hollow nanosphere units of CoSe₂ and CoSe nanocrystalline. CoSe₂/CoSe bird nests achieve excellent cycling performance, high reversible capacity and satisfactory rate capability (1361 mAh/g at 1 A/g after 1000 cycles, 579 mAh/g at 2 A/g after 2000 cycles, 315 mAh/g at 5 A/g after 1000 cycles). Electrochemical kinetics analyses and ex-situ material characterization reveal that the surface capacitive behavior controls the electrochemical reaction, and the composite has low reaction impedance, fast and stable Li⁺ diffusion, and superior structural stability. The superior lithium storage performance is attributed to the unique superstructure bird nest. Large specific surface area, abundant hierarchical pores and the opening mouth result in high electrochemical activity, which induces high reversible capacity. The small hollow nanosphere units, the sufficiently thick hierarchical porous superstructure shell and the large hollow interior bring about the strong synergistic effect to improve cycling performance. The intimately coupling of CoSe₂/CoSe nanocrystalline and the hollow nanosphere units guarantees high conductivity. This work has greatly enriched the understanding of structure design of high-performance cobalt selenide anodes.

Synthesis of MnO/C/Co3O4 nanocomposites by a Mn2+-oxidizing bacterium as a biotemplate for lithium-ion batteries

The biotemplate and bioconversion strategy represents a sustainable and environmentally friendly approach to material manufacturing. In the current study, biogenic manganese oxide aggregates of the Mn²⁺-oxidizing bacterium Pseudomonas sp. T34 were used as a precursor to synthesize a biocomposite that incorporated Co (CMC-Co) under mild shake-flask conditions based on the biomineralization process of biogenic Mn oxides and the characteristics of metal ion subsidies. X-ray photoelectron spectroscopy, phase composition and fine structure analyses demonstrated that hollow MnO/C/Co₃O₄ multiphase composites were fabricated after high-temperature annealing of the biocomposites at 800°C. The cycling and rate performance of the prepared anode materials for lithium-ion batteries were compared. Due to the unique hollow structure and multiphasic state, the reversible discharge capacity of CMC-Co remained at 650 mAh g^-1 after 50 cycles at a current density of 0.1 Ag^-1, and the coulombic efficiency remained above 99% after the second cycle, indicating a good application potential as an anode material for lithium-ion batteries.

A robust, highly reversible, mixed conducting sodium metal anode

Sodium metal anode holds great promise in pursuing high-energy and sustainable rechargeable batteries, but severely suffers from fatal dendrite growth accompanied with huge volume change. Herein, a robust mixed conducting sodium metal anode is designed through incorporating NaSICON-type solid Na-ion conductor into bulk Na. A fast and continuous pathway for simultaneous transportation of electrons and Na⁺ is established throughout the composite anode. The intimate contact between Na-ion conducting phase and Na metallic phase constructs abundant two-phase boundaries for fast redox reactions. Further, the compact configuration of the composite anode substantially protects Na metal from being corroded by liquid organic electrolyte for the minimization of side reactions. Benefiting from the unique configuration, the composite anode shows highly reversible and durable Na plating/stripping behavior. The symmetric cells exhibit ultralong lifespan for over 700 h at 1 mA cm^-2 with a high capacity of 5 mAh cm^-2 and outstanding rate capability up to 8 mA cm^-2 in the carbonate electrolyte. Full cells with Na₃V₂(PO₄)₃/C cathode demonstrate impressive cycling stability (capacity decay of 0.012% per cycle) and low charge/discharge polarization as well. This work provides new insights into rational design and development of robust sodium metal anode through an architecture engineering strategy for advanced rechargeable sodium batteries.