Peter B. Hallac

Multilayered Si Nanoparticle/Reduced Graphene Oxide Hybrid as a High‐Performance Lithium‐Ion Battery Anode

Multilayered Si/RGO anode nanostructures, featuring alternating Si nanoparticle (NP) and RGO layers, good mechanical stability, and high electrical conductivity, allow Si NPs to easily expand between RGO layers, thereby leading to high reversible capacity up to 2300 mAh g(-1) at 0.05 C (120 mA g(-1) ) and 87% capacity retention (up to 630 mAh g(-1) ) at 10 C after 152 cycles.

Controllable Synthesis of Hollow Si Anode for Long‐Cycle‐Life Lithium‐Ion Batteries

DOI: 10.1002/adma.201400578 Here, we report a facile, surfactant-free method to prepare hollow Si with tunable morphology from hollow cubes, spheres, tubes, to fl owers and other shapes. Figure 1 a illustrates the controllable synthesis of hollow Si materials. We controllably synthesized various carbonates, followed by Si deposition and removal of carbonate templates by washing in a dilute hydrochloric acid. Hollow Si with various morphologies was obtained, including cubes, spheres, tubes, and fl owers. Carbonates have not been reported as templates for fabrication of hollow Si until now, which is likely due to potential reactions between carbonates and Si; for example, thermodynamic calculations indicate the changes in Gibbs free energies are −97.7, −95.2, and −94.7 kCal mol −1

A Hierarchical Tin/Carbon Composite as an Anode for Lithium-Ion Batteries with a Long Cycle Life**

Tin is a promising anode candidate for next-generation lithium-ion batteries with a high energy density, but suffers from the huge volume change (ca. 260 %) upon lithiation. To address this issue, here we report a new hierarchical tin/carbon composite in which some of the nanosized Sn particles are anchored on the tips of carbon nanotubes (CNTs) that are rooted on the exterior surfaces of micro-sized hollow carbon cubes while other Sn nanoparticles are encapsulated in hollow carbon cubes. Such a hierarchical structure possesses a robust framework with rich voids, which allows Sn to alleviate its mechanical strain without forming cracks and pulverization upon lithiation/de-lithiation. As a result, the Sn/C composite exhibits an excellent cyclic performance, namely, retaining a capacity of 537 mAh g(-1) for around 1000 cycles without obvious decay at a high current density of 3000 mA g(-1) .

Improved Cyclic Performance of Si Anodes for Lithium-Ion Batteries by Forming Intermetallic Interphases between Si Nanoparticles and Metal Microparticles

Silicon, an anode material with the highest capacity for lithium-ion batteries, needs to improve its cyclic performance prior to practical applications. Here, we report on a novel design of Si/metal composite anode in which Si nanoparticles are welded onto surfaces of metal particles by forming intermetallic interphases through a rapid heat treatment. Unlike pure Si materials that gradually lose electrical contact with conductors and binders upon repeated charging and discharging cycles, Si in the new Si/metal composite can maintain the electrical contact with the current collector through the intermetallic interphases, which are inactive and do not lose physical contact with the conductors and binders, resulting in significantly improved cyclic performance. Within 100 cycles, only 23.8% of the capacity of the pure Si anode is left while our Si/Ni anode obtained at 900 °C maintains 73.7% of its capacity. Therefore, the concept of employing intermetallic interphases between Si nanoparticles and metal particles provides a new avenue to improve the cyclic performance of Si-based anodes.

Improving cyclic performance of Si anode for lithium-ion batteries by forming an intermetallic skin

An intermetallic NiSix coating layer was introduced on the Si surface by sputtering Ni onto Si, followed by heat-treatment. The resulting chemically bonded NiSix layer, unlike physically coated layers that typically can crack and detach from Si surfaces upon repeated cycling, remains connected with the bulk Si as a skin-like protective surface.