Dense T-Nb2O5/Carbon Microspheres for Ultrafast-(Dis)charge and High-Loading Lithium-Ion Batteries

Orthorhombic niobium pentoxide (T-Nb2O5) is regarded as a potential anode material for lithium-ion batteries (LIBs) due to ultrafast charge/discharge and high safety. However, the poor electronic conductivity and low mass loading of nanostructured T-Nb2O5 limit its practical application in LIBs. Herein, we design and construct dense microspheres consisting of nanostructured T-Nb2O5 embedded in amorphous N-doped carbon (Nb2O5@NC) via a facile method to achieve fast ionic and electronic transport as well as a high mass loading. The dense micro-sized particles with an interconnected carbon network avoid the low mass loading and volumetric energy density of conventional nanostructures. Interconnected pores in the range of a few nanometers are also formed in the Nb2O5@NC microspheres. Notably, at a high mass loading of 12.8 mg cm-2, Nb2O5@NC can achieve a high specific capacity of 171.5 mAh g-1 and an areal capacity of 2.05 mAh cm-2, showing its high lithium storage capacity. The intercalation reaction mechanism with a small volume change during cycling at both crystal lattice and microsphere levels is confirmed by in situ X-ray diffraction and in situ high-resolution transmission electron microscopy. The elegant structure and the electrochemical reaction mechanism disclosed in the work is important for designing ultrafast-(dis)charge electrode materials.

Fabrication of Lithium Indolide and Derivates for Ion Conduction

The development of ionic conductors as solid-state electrolytes to replace the widely used liquid electrolytes could effectively solve the safety issues as well as enhance the energy density of batteries. Yet no ionic conductors to date could meet all the criteria of solid-state electrolytes for practical applications. Therefore, exploration of new materials is highly demanded. Herein, a new type of metalorganic-based materials, namely, lithium indolide and its tetrahydrofuran (THF)-coordinated derivatives, are developed and employed as fast ionic conductors. Their crystal structures are also determined. Particularly, the lithium indolide ditetrahydrofuran shows ionic conductivities of 6.28 × 10^-6 and 8.27 × 10^-4 S cm^-1 at 110 and 150 °C, respectively. A "neutral ligand-assisted" cation migration mechanism is proposed, where the migration of Li⁺ may be facilitated by the dynamic equilibrium of the neutral ligand and the large sized anions. The present idea of using metalorganic compounds coordinated with neutral ligands for fast ionic conductors provides vast opportunities for discovering new solid-state electrolytes in the future thanks to the rich chemistry of organic anions and ligands.

Construction of Cu7KS4@NixCo1-x(OH)2 Nano-Core-Shell Structures with High Conductivity and Multi-Metal Synergistic Effect for Superior Hybrid Supercapacitors

Reasonable design of materials with complex nanostructures and diverse chemical compositions is of great significance in the field of energy storage. Cu₇KS₄ (CKS) is considered a potential electrode material for supercapacitors due to its superior electrical conductivity. Transition metal hydroxides are widely used as electrode materials for supercapacitors due to their high theoretical specific capacitance (C_s); however, single metal species with limited active sites restrict their further applications for energy storage. Herein, through a hydrothermal reaction, CKS nanorods were prepared, and then binary metal hydroxide Ni_xCo_1-x(OH)₂ nanosheets were generated directly on CKS nanorods through a one-step hydrothermal reaction to form a nano-core-shell structure (NCSS). By regulating the mole ratio of nickel nitrate to cobalt nitrate, the resulting Ni_0.75Co_0.25(OH)₂ nanosheets with the best electrochemical activity were prepared and supported on CKS nanorods to form a CKS@N_0.75C_0.25OH NCSS. The as-prepared CKS@N_0.75C_0.25OH NCSS has a larger specific surface area, which can provide more active sites, while the abundant metal species composition can generate abundant redox reactions to boost the pseudocapacitance. The prepared CKS@N_0.75C_0.25OH/NF electrode exhibits outstanding specific capacitance and cycle life. The assembled CKS@N_0.75C_0.25OH/NF//AC all-solid-state asymmetric supercapacitor achieves a high energy density of 88.7 Wh kg^-1 at a power density of 849.9 W kg^-1 with superior cycle life. Therefore, the use of polymetallic hydroxides to construct NCSS electrodes has great research significance and broad application prospects.

Understanding the Aging Mechanism of Na-Based Layered Oxide Cathodes with Different Stacking Structures

Manganese-based layered oxides are one of the most promising cathodes for Na-ion batteries, but the prospect of their practical application is challenged by high sensitivity to ambient air. The stacking structure of materials is critical to the aging mechanism between layered oxides and air, but there remains a lack of systematic study. Herein, comprehensive research on model materials P-type Na0.50MnO2 and O-type Na0.85MnO2 reveals that the O-phase displays a much higher dynamic affinity toward moisture air compared to P-type compounds. For air-exposed O-type material, Na+ ions are extracted from the crystal lattice to form alkaline species at the surface in contact with air, accompanying by the increase of the valence state of transition metals. The series of undesired reactions result in an increase of interfacial resistance and huge capacity loss. Comparatively, the insertion of H2O into the Na layer is the main reaction during air-exposure of P-type material, and the inserted H2O can be extracted by high-temperature treatment. The H2O de/insertion process not only causes no performance degradation but also can enlarge the interlayer distance. With these understandings, we further propose a washing-resintering strategy to recover the performance of aged O-type materials and an aging strategy to build high-performance P-type materials.

Long-Life and Highly Utilized Zinc Anode for Aqueous Batteries Enabled by Electrolyte Additives with Synergistic Effects

After decades of development, zinc-based batteries with the advantages of high energy density, low cost, and environmental benignity have been considered as a promising battery system in the application of energy storage. However, the poor cycle performance of zinc anode strongly restricts the cycle life of zinc-based batteries and thus limits its large-scale application. Electrolyte additives have been proven to be one of the most straightforward strategies in improving the stability of zinc anode during cycles, while the options of additives are still limited. This work is based on the in-depth investigation of the electrochemical behavior of both the organic additives and the zinc species in the electrolyte. The modification effects of poly(vinyl alcohol) (PVA) and vanillin as two typical additives from the electroplating industry in both the zinc plating and zinc anode are systematically studied. It is revealed that PVA could increase the utilization and rate performance of the anode, while greatly promoting the corrosion and shape change of the zinc anode. On the contrary, the existence of vanillin could maintain the structure of the anode during cycles, while the rate performance of the battery is hindered. With the coaddition of the PVA and vanillin, the zinc anode shows superior performance in cycle life, rate performance, active material utilization, and discharge energy retention. These findings provide insight for the enrichment of electrolyte additives in zinc-based batteries.