Emma Mullane

High-Performance Germanium Nanowire-Based Lithium-Ion Battery Anodes Extending over 1000 Cycles Through in Situ Formation of a Continuous Porous Network

Here we report the formation of high-performance and high-capacity lithium-ion battery anodes from high-density germanium nanowire arrays grown directly from the current collector. The anodes retain capacities of ∼ 900 mAh/g after 1100 cycles with excellent rate performance characteristics, even at very high discharge rates of 20-100C. We show by an ex situ high-resolution transmission electron microscopy and high-resolution scanning electron microscopy study that this performance can be attributed to the complete restructuring of the nanowires that occurs within the first 100 cycles to form a continuous porous network that is mechanically robust. Once formed, this restructured anode retains a remarkably stable capacity with a drop of only 0.01% per cycle thereafter. As this approach encompasses a low energy processing method where all the material is electrochemically active and binder free, the extended cycle life and rate performance characteristics demonstrated makes these anodes highly attractive for the most demanding lithium-ion applications such as long-range battery electric vehicles.

Atomically Abrupt Silicon–Germanium Axial Heterostructure Nanowires Synthesized in a Solvent Vapor Growth System

The growth of Si/Ge axial heterostructure nanowires in high yield using a versatile wet chemical approach is reported. Heterostructure growth is achieved using the vapor zone of a high boiling point solvent as a reaction medium with an evaporated tin layer as the catalyst. The low solubility of Si and Ge within the Sn catalyst allows the formation of extremely abrupt heterojunctions of the order of just 1-2 atomic planes between the Si and Ge nanowire segments. The compositional abruptness was confirmed using aberration corrected scanning transmission electron microscopy and atomic level electron energy loss spectroscopy. Additional analysis focused on the role of crystallographic defects in determining interfacial abruptness and the preferential incorporation of metal catalyst atoms near twin defects in the nanowires.

A Rapid, Solvent-Free Protocol for the Synthesis of Germanium Nanowire Lithium-Ion Anodes with a Long Cycle Life and High Rate Capability

A rapid synthetic protocol for the formation of high-performance Ge nanowire-based Li-ion battery anodes is reported. The nanowires are formed in high density by the solvent-free liquid deposition of a Ge precursor directly onto a heated stainless steel substrate under inert conditions. The novel growth system exploits the in situ formation of discrete Cu3Ge catalyst seeds from 1 nm thermally evaporated Cu layers. As the nanowires were grown from a suitable current collector, the electrodes could be used directly without binders in lithium-ion half cells. Electrochemical testing showed remarkable capacity retention with 866 mAh/g achieved after 1900 charge/discharge cycles and a Coulombic efficiency of 99.7%. The nanowire-based anodes also showed high-rate stability with discharge capacities of 800 mAh/g when cycled at a rate of 10C.

Solution phase synthesis of silicon and germanium nanowires

Si and Ge nanowires have attracted widespread interest due to their suitability for photovoltaic, nanoelectronic, sensing and energy storage applications. As a result, a variety of synthetic protocols have emerged which include chemical vapour deposition and solution phase approaches. Early solution based approaches were hindered by the high nucleation temperatures required for Ge and Si NW formation but these have been overcome by using either supercritical fluid (SCF) approaches or high boiling point organic solvent (HBS) routes. This feature article examines the various synthetic strategies which have been successful in forming Ge and Si NWs within solvent based systems with particular emphasis on the reaction media and catalytic method employed.

High density and patternable growth of silicon, germanium and alloyed SiGe nanowires by a rapid anneal protocol

We report the formation of silicon, germanium and alloyed Si1−xGex nanowires by direct pyrolysis of liquid precursors on a heated substrate in an inert environment. The nanowires form in high density on the substrate with a fast reaction time. We use SEM, HRTEM, EDX-STEM, and Raman spectroscopy to carry out an in depth study into the population distribution of Si1−xGex nanowires. The method was sufficiently adaptable to pattern the nanowire growth using standard dry film lithography techniques. Additionally, we further show that direct writing with a copper metal pen deposited sufficient catalyst to allow localised nanowire growth constrained to the treated areas.

GREENLION Project: Advanced Manufacturing Processes for Low Cost Greener Li-Ion Batteries

GREENLION is a Large Scale Collaborative Project within the FP7 (GC.NMP.2011-1) leading to the manufacturing of greener and cheaper Li-Ion batteries for electric vehicle applications via the use of water soluble, fluorine-free, high thermally stable binders, which would eliminate the use of VOCs and reduce the cell assembly cost. The project has 6 key objectives: (i) development of new active and inactive battery materials viable for water processes (green chemistry); (ii) development of innovative processes (coating from aqueous slurries) capable of reducing electrode production cost and avoid environmental pollution; (iii) development of new assembly procedures (including laser cutting and high temperature pre-treatment) capable of substantially reduce the time and the cost of cell fabrication; (iv) lighter battery modules with easier disassembly through eco-designed bonding techniques; (v) waste reduction, which, by making use of the water solubility of the binder, allows the extensive recovery of the active and inactive battery materials; and (vi) development of automated process and construction of fully integrated battery module for electric vehicle applications with optimized electrodes, cells, and other ancillaries. Achievements during the first 18 months of the project, especially on materials development and water-based electrode fabrication are reported herein.