Bernhard M. Metz

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) .

Effect of Calendering on Electrode Wettability in Lithium-Ion Batteries

Controlling the wettability between the porous electrode and the electrolyte in lithium ion batteries can improve both the manufacturing process and the electrochemical performance of the cell. The wetting rate, which is the electrolyte transport rate in the porous electrode, can be quantified using the wetting balance. The effect of the calendering process on the wettability of anode electrodes was investigated. A graphite anode film with an as-coated thickness of 59 μm was used as baseline electrode film and was calendered to produce films with thickness ranging from 55 to 41 µm. Results show that wettability is improved by light calendering from an initial thickness of 59 μm to a calendered thickness of 53 μm where the wetting rate increased from 0.375 to 0.589 mm/s0.5. Further calendering below 53 µm resulted in a decrease in wetting rates to a minimum observed value of 0.206 mm/s0.5 at a calendered thickness of 41 μm. Under the same electrolyte, wettability of the electrode is controlled to a great extent by the pore structure in the electrode film which includes parameters such as porosity, pore size distribution, pore geometry and topology. Relations between the wetting behavior and the pore structure as characterized by mercury intrusion and electron microscopy exist and can be used to manipulate the wetting behavior of electrodes.

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.