Germanium Silicon Alloy Anode Material Capable of Tunable Overpotential by Nanoscale Si Segregation

Abstract

ABSTRACT:We developed the novel electrode that enables fine control of overpotential by exploiting surface segregation that is the enrichment of one component at the surface of binary alloy. To realize this approach, we controlled the proportion of Si with low Li diffusivity at the surface by annealing the SiGe nanowire in H 2 environment at various temperatures. The resulting SiGe nanowires annealed at 850°C exhibited high reversible capacity (>1031 mA·h·g −1 ), and long cycle life (400 cycles) with high capacity retention (89.0%) at 0.2 C. This superior battery performance is attributed to the remaining unlithiated part acting as support frame to prevent pulverization of anode material, which results from the fine-tuning of overpotential by controlling the degree of Si segregation.

Electrolytic Formation of Crystalline Silicon/Germanium Alloy Nanotubes and Hollow Particles with Enhanced Lithium‐Storage Properties

“…[14][15][16][17][18][19] However,d ramatic volume changes associated with the lithium insertion and extraction reactions (up to 400 %) lead to pulverization of the Si/Ge based materials and thus poor cycling life of electrodes. [20] One typical approach to overcome this problem is the design and synthesis of complex micro-/nanostructured electrodes that can maintain their structural integration after many cycles. [21] Notably,adiversity of hollow nanostructures with distinct geometric shapes,s uch as nanotubes or hollow spheres has been extensively investigated.…”

“…[9,[35][36][37][38] Thed riving force of solid diffusion in ab inary alloy is generally explained as minimization of total Gibbs free energy and the presence of Ge at the surface of the SiGe alloy is energetically favorable because Ge has lower surface energy than Si. [20] Hence,t he outward diffusion of Ge species is faster than the inward diffusion of Si species in the Ge@Si core-shell nanowires,thus generating internal voids.Asaresult, the transformation from the core-shell Ge@Si nanowires to SiGe alloy nanotubes is favorable.…”

Kirkendall void formation in reverse step graded Si1−xGex/Ge/Si(001) virtual substrates

“…Due to the extremely low inter-diffusion rates of Si and Ge [7,8], this effect is reported to occur mostly in nanowire and nanosphere structures [9] that use extended annealing [10,11] or electro-reduction of SiO 2 and GeO 2 (e.g. to create SiGe nanotubes for Li-ion battery electrode applications [12]) with minor developments in thin film [13].…”

Germanium Nanograin Decoration on Carbon Shell: Boosting Lithium‐Storage Properties of Silicon Nanoparticles

“…In order to take full advantage of Si and Ge synchronously, heterogeneous structures consisting of Si and Ge have been constructed to modify their physicochemical properties, mechanics, and kinetics associated with lithium, thus optimizing their electrochemical performance . Benefiting by the highest theoretical capacity of Si anode, the component Si attributes to high overall capacity of the electrode.…”

“…During the lithiation process, Ge component would initially begin to react with Li from 0.5 V, followed by the lithiation reaction of Si at ≈0.2 V. Thus the strain–stress generated by volume expansion of Ge and Si could be released subsequently, improving the structural and electrical integrity of the electrode based on this synergistic effect. Until now, little research achievement has been made on this heterogeneous Si/Ge, including Si/Ge nanocomposites, Si/Ge core–shell nanowires, Si/Ge alloy, Si/Ge nanotubes . However, the dramatic volume changes of these heterohybrids are still evident, which lead to pulverization of the Si/Ge anodes and thus poor cycling life.…”