Jun Pu

Structure design of NiCo2O4 electrodes for high performance pseudocapacitors and lithium-ion batteries

High capacitance/capacity electrodes are in urgent demand to increase the charge storage capability of energy storage devices. However, there are some scientific and technical challenges for a large amount of charges to be transported through the devices because the kinetic resistances and volume change issues may limit the performance of devices. 3D conductive scaffolds are usually developed to build rapid electron/ion pathways and accommodate volume changes. Using a templated electrodeposition and hydrothermal synthesis technique, we developed a composite electrode consisting of NiCo2O4 nanowires on ultralight nickel foam. The NiCo2O4 nanowires provide a large surface for rapid charge transports. The ultralight nickel foam electrically wires NiCo2O4 and accommodates the volume expansion of NiCo2O4 during lithiation. The composite electrode demonstrates a high performance microstructure for ideal pseudocapacitors and lithium ion anodes. It not only enhances the utilization of active materials but also increases the electrode based specific capacitance by one order of magnitude as compared to the widely used nickel foam. More importantly, the ultralight nickel foam supported structure could further be extended to other high capacitance/capacity metal oxide materials for pseudocapacitors and lithium-ion battery applications.

Novel Co2VO4 Anodes Using Ultralight 3D Metallic Current Collector and Carbon Sandwiched Structures for High-Performance Li-Ion Batteries

A novel spinel Co2 VO4 is studied as the Li-ion battery anode material and it is sandwiched with a 3D ultralight porous current collector (PCC) and amorphous carbon. Co2 VO4 demonstrates the high capacity and excellent cyclability because of the mixed lithium storage mechanisms. The 3D composite structure requires no binders and replaces the conventional current collector (Cu foil) with a 3D ultralight porous metal scaffold, yielding the high electrode-based capacity. Such a novel composite anode also enables the close adhesion of Co2 VO4 to the PCC scaffold. The resulting monolithic electrode has the rapid electron pathway and stable mechanical properties, which lead to the excellent rate capabilities and cycling properties. At a current density of 1 A g-1 , the PCC and carbon sandwiched Co2 VO4 anode is able to deliver a stable reversible capacity of about 706.8 mAh g-1 after 1000 cycles. Generally, this study not only develops a new Co2 VO4 anode with high capacity and good cyclability, but also demonstrates an alternative approach to improve the electrochemical properties of high capacity anode materials by using ultralight porous metallic current collector instead of heavy copper foil.

Porous-Nickel-Scaffolded Tin–Antimony Anodes with Enhanced Electrochemical Properties for Li/Na-Ion Batteries

The energy and power densities of rechargeable batteries urgently need to be increased to meet the ever-increasing demands of consumer electronics and electric vehicles. Alloy anodes are among the most promising candidates for next-generation high-capacity battery materials. However, the high capacities of alloy anodes usually suffer from some serious difficulties related to the volume changes of active materials. Porous supports and nanostructured alloy materials have been explored to address these issues. However, these approaches seemingly increase the active material-based properties and actually decrease the electrode-based capacity because of the oversized pores and heavy mass of mechanical supports. In this study, we developed an ultralight porous nickel to scaffold with high-capacity SnSb alloy anodes. The porous-nickel-supported SnSb alloy demonstrates a high specific capacity and good cyclability for both Li-ion and Na-ion batteries. Its capacity retains 580 mA h g-1 at 2 A g-1 after 100 cycles in Li-ion batteries. For a Na-ion battery, the composite electrode can even deliver a capacity of 275 mA h g-1 at 1 A g-1 after 1000 cycles. This study demonstrates that combining the scaffolding function of ultralight porous nickel and the high capacity of the SnSb alloy can significantly enhance the electrochemical performances of Li/Na-ion batteries.

In situ surface engineering of nickel inverse opal for enhanced overall electrocatalytic water splitting

High-efficiency non-precious catalysts are important for hydrogen and oxygen evolution reactions (HER and OER). Practical water splitting needs not only intrinsically active catalyst materials but also the maximization of their electrocatalytic capability in a real electrolyzer. Here, we report for the first time a Ni/Ni2P inverse opal architecture fabricated by surface engineering. The superior HER properties are enabled by maximum active crystallographic plane exposure and vertical alignment of Ni2P nanosheets on nickel inverse opal. It requires an overpotential of only 73 mV to drive a HER current density of −20 mA cm−2. After doping with Fe, the resulting Fe:Ni/Ni2P inverse electrode shows excellent OER performance with a very low overpotential (285 mV) at a current density of 20 mA cm−2. An alkaline electrolyzer using the two 3D structured electrodes could split water at 20 mA cm−2 with a low voltage of ∼1.52 V for 100 h. The catalytic activity is even superior to that of the noble metal catalyst couple (IrO2–Pt/C). This work provides a surface engineered opal structure to maximize the electrocatalyst properties in the systems with coupled electron transfer and mass transport.

Low Interface Energies Tune the Electrochemical Reversibility of Tin Oxide Composite Nanoframes as Lithium-Ion Battery Anodes

The conversion reaction of lithia can push up the capacity limit of tin oxide-based anodes. However, the poor reversibility limits the practical applications of lithia in lithium-ion batteries. The latest reports indicate that the reversibility of lithia has been appropriately promoted by compositing tin oxide with transition metals. The underlying mechanism is not revealed. To design better anodes, we studied the nanostructured metal/Li2O interfaces through atomic-scale modeling and proposed a porous nanoframe structure of Mn/Sn binary oxides. The first-principles calculation implied that because of a low interface energy of metal/Li2O, Mn forms smaller particles in lithia than Sn. Ultrafine Mn nanoparticles surround Sn and suppress the coarsening of Sn particles. Such a composite design and the resultant interfaces significantly enhance the reversible Li-ion storage capabilities of tin oxides. The synthesized nanoframes of manganese tin oxides exhibit an initial capacity of 1620.6 mA h g-1 at 0.05 A g-1. Even after 1000 cycles, the nanoframe anode could deliver a capacity of 547.3 mA h g-1 at 2 A g-1. In general, we demonstrated a strategy of nanostructuring interfaces with low interface energy to enhance the Li-ion storage capability of binary tin oxides and revealed the mechanism of property enhancement, which might be applied to analyze other tin oxide composites.