Iso-Oriented NaTi₂(PO₄)₃ Mesocrystals as Anode Material for High-Energy and Long-Durability Sodium-Ion Capacitor

Sodium-ion capacitors (SIC) combine the merits of both high-energy batteries and high-power electrochemical capacitors as well as the low cost and high safety. However, they are also known to suffer from the severe deficiency of suitable electrode materials with high initial Coulombic efficiency (ICE) and kinetic balance between both electrodes. Herein, we report a facile solvothermal synthesis of NaTi₂(PO₄)₃ nanocages constructed by iso-oriented tiny nanocrystals with a mesoporous architecture. It is notable that the NaTi₂(PO₄)₃ mesocrystals exhibit a large ICE of 94%, outstanding rate capability (98 mA h g^–1 at 10 C), and long cycling life (over 77% capacity retention after 10 000 cycles) in half cells, all of which are in favor to be utilized into a full cell. When assembled with commercial activated carbon to an SIC, the system delivers an energy density of 56 Wh kg^–1 at a power density of 39 W kg^–1. Even at a high current rate of 5 A g^–1 (corresponds to finish a full charge/discharge process in 2 min), the SIC still works well after 20 000 cycles without obvious capacity degradation. With the merits of impressive energy/power densities and longevity, the obtained hybrid capacitor should be a promising device for highly efficient energy storage systems

Amorphous ZnO Quantum Dot/Mesoporous Carbon Bubble Composites for a High-Performance Lithium-Ion Battery Anode

Due to its high theoretical capacity (978 mA h g^–1), natural abundance, environmental friendliness, and low cost, zinc oxide is regarded as one of the most promising anode materials for lithium-ion batteries (LIBs). A lot of research has been done in the past few years on this topic. However, hardly any research on amorphous ZnO for LIB anodes has been reported despite the fact that the amorphous type could have superior electrochemical performance due to its isotropic nature, abundant active sites, better buffer effect, and different electrochemical reaction details. In this work, we develop a simple route to prepare an amorphous ZnO quantum dot (QDs)/mesoporous carbon bubble composite. The composite consists of two parts: mesoporous carbon bubbles as a flexible skeleton and monodisperse amorphous zinc oxide QDs (smaller than 3 nm) encapsulated in an amorphous carbon matrix as a continuous coating tightly anchored on the surface of mesoporous carbon bubbles. With the benefits of abundant active sites, amorphous nature, high specific surface area, buffer effect, hierarchical pores, stable interconnected conductive network, and multidimensional electron transport pathways, the amorphous ZnO QD/mesoporous carbon bubble composite delivers a high reversible capacity of nearly 930 mA h g^–1 (at current density of 100 mA g^–1) with almost 90% retention for 85 cycles and possesses a good rate performance. This work opens the possibility to fabricate high-performance electrode materials for LIBs, especially for amorphous metal oxide-based materials

Hollow Ball-in-Ball Co_<i>x</i>Fe_3–<i>x</i>O₄ Nanostructures: High-Performance Anode Materials for Lithium-Ion Battery

The intrinsic electronic conductivity can be improved by doping efficiently. Co_<i>x</i>Fe_3–<i>x</i>O₄ nanostructures have been synthesized for the first time to improve the conductivity of lithium battery electrode. The solid solution Co_<i>x</i>Fe_{3–<i>‑</i>x}O₄ were characterized by X-ray diffraction pattern (XRD), Raman spectrum, scanning electron microscopy (SEM), transmission electron microscope (TEM), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV). The results show that the doping enlarge the lattice spacing but the structure of Co₃O₄ is stable in the Li-ion intercalation/deintercalation process. The AC impedance spectrum reveals the conductivity is well improved. In addition, the solid solution Co_<i>x</i>Fe_3–<i>x</i>O₄ exhibit excellent electrochemical characteristics. The electrodes with 20% molar ratio of Fe ions own a reversible capacity of 650.2 mA h g^–1 at a current density of 1 A g^–1 after 100 cycles

Free-Standing and Transparent Graphene Membrane of Polyhedron Box-Shaped Basic Building Units Directly Grown Using a NaCl Template for Flexible Transparent and Stretchable Solid-State Supercapacitors

Transparency has never been integrated into freestanding flexible graphene paper (FF-GP), although FF-GP has been discussed extensively, because a thin transparent graphene sheet will fracture easily when the template or substrate is removed using traditional methods. Here, transparent FF-GP (FFT-GP) was developed using NaCl as the template and was applied in transparent and stretchable supercapacitors. The capacitance was improved by nearly 1000-fold compared with that of the laminated or wrinkled chemical vapor deposition graphene-film-based supercapacitors