Zaiyuan Le

Pseudocapacitive Sodium Storage in Mesoporous Single-Crystal-like TiO2–Graphene Nanocomposite Enables High-Performance Sodium-Ion Capacitors

Sodium-ion capacitors can potentially combine the virtues of high power capability of conventional electrochemical capacitors and high energy density of batteries. However, the lack of high-performance electrode materials has been the major challenge of sodium-based energy storage devices. In this work, we report a microwave-assisted synthesis of single-crystal-like anatase TiO2 mesocages anchored on graphene as a sodium storage material. The architecture of the nanocomposite results in pseudocapacitive charge storage behavior with fast kinetics, high reversibility, and negligible degradation to the micro/nanostructure. The nanocomposite delivers a high capacity of 268 mAh g-1 at 0.2 C, which remains 126 mAh g-1 at 10 C for over 18 000 cycles. Coupling with a carbon-based cathode, a full cell of sodium-ion capacitor successfully demonstrates a high energy density of 64.2 Wh kg-1 at 56.3 W kg-1 and 25.8 Wh kg-1 at 1357 W kg-1, as well as an ultralong lifespan of 10 000 cycles with over 90% of capacity retention.

Hierarchical Nanostructured WO3 with Biomimetic Proton Channels and Mixed Ionic-Electronic Conductivity for Electrochemical Energy Storage

Protein channels in biologic systems can effectively transport ions such as proton (H(+)), sodium (Na(+)), and calcium (Ca(+)) ions. However, none of such channels is able to conduct electrons. Inspired by the biologic proton channels, we report a novel hierarchical nanostructured hydrous hexagonal WO3 (h-WO3) which can conduct both protons and electrons. This mixed protonic-electronic conductor (MPEC) can be synthesized by a facile single-step hydrothermal reaction at low temperature, which results in a three-dimensional nanostructure self-assembled from h-WO3 nanorods. Such a unique h-WO3 contains biomimetic proton channels where single-file water chains embedded within the electron-conducting matrix, which is critical for fast electrokinetics. The mixed conductivities, high redox capacitance, and structural robustness afford the h-WO3 with unprecedented electrochemical performance, including high capacitance, fast charge/discharge capability, and very long cycling life (>50,000 cycles without capacitance decay), thus providing a new platform for a broad range of applications.

Regenerative Polysulfide-Scavenging Layers Enabling Lithium–Sulfur Batteries with High Energy Density and Prolonged Cycling Life

Lithium-sulfur batteries, notable for high theoretical energy density, environmental benignity, and low cost, hold great potential for next-generation energy storage. Polysulfides, the intermediates generated during cycling, may shuttle between electrodes, compromising the energy density and cycling life. We report herein a class of regenerative polysulfide-scavenging layers (RSL), which effectively immobilize and regenerate polysulfides, especially for electrodes with high sulfur loadings (e.g., 6 mg cm-2). The resulting cells exhibit high gravimetric energy density of 365 Wh kg-1, initial areal capacity of 7.94 mAh cm-2, low self-discharge rate of 2.45% after resting for 3 days, and dramatically prolonged cycling life. Such blocking effects have been thoroughly investigated and correlated with the work functions of the oxides as well as their bond energies with polysulfides. This work offers not only a class of RSL to mitigate shuttling effect but also a quantified design framework for advanced lithium-sulfur batteries.

Encapsulation of SnO2 nanocrystals into hierarchically porous carbon by melt infiltration for high-performance lithium storage

A simple and scalable melt infiltration method has been developed to encapsulate SnO2 nanocrystals into a hierarchically porous carbon matrix as a high-capacity lithium storage material. SnO2 nanocrystals in a three-dimensional carbonaceous network are obtained via melt infiltration of SnCl2 and subsequent in situ conversion. The SnO2–carbon composite delivers high capacity with a long lifespan of over 800 cycles. Such a method provides an efficient strategy to encapsulate active materials into porous carbons with superior electrochemical performance.

Prussian Blue Analogue with Fast Kinetics Through Electronic Coupling for Sodium Ion Batteries

Alternative battery systems based on the chemistry of sodium are being considered to offer sustainability and cost-effectiveness. Herein, a simple and new method is demonstrated to enable nickel hexacyanoferrate (NiHCF) Prussian blue analogues (PBA) nanocrystals to be an excellent host for sodium ion storage by functionalization with redox guest molecule. The method is achieved by using NiHCF PBA powders infiltrated with the 7,7,8,8-tetracyanoquinododimethane (TCNQ) solution. Experimental and ab initio calculations results suggest that TCNQ molecule bridging with Fe atoms in NiHCF Prussian blue analogue leads to electronic coupling between TCNQ molecules and NiHCF open-framework, which functions as an electrical highway for electron motion and conductivity enhancement. Combining the merits including high electronic conductivity, open framework structure, nanocrystal, and interconnected mesopores, the NiHCF/TCNQ shows high specific capacity, fast kinetics and good cycling stability, delivering a high specific capacity of 35 mAh g-1 after 2000 cycles, corresponding a capacity loss of 0.035% decay per cycle.

Better lithium-ion storage materials made through hierarchical assemblies of active nanorods and nanocrystals

Lithium-ion storage materials with significantly improved performance were developed through the hierarchical assemblies of vanadium-based oxide (V2O5 and LiV3O8) nanorods or iron oxide (Fe3O4) nanocrystals using an efficient, continuous aerosol-spray process. Such hierarchically porous spheres, which were made from networks of low-dimension building blocks, result in materials with reduced ion-diffusion length, fast electrolyte diffusion, and structural robustness. Due to their unique hierarchical structure, these spheres exhibit high lithium storage capacity, excellent cycling stability and good rate capability. This work presents a novel synthesis approach toward better lithium-ion storage materials.