Quantum Confinement and Its Related Effects on the Critical Size of GeO₂ Nanoparticles Anodes for Lithium Batteries

Abstract

This work has been performed to determine the critical size of the GeO2 nanoparticle for lithium battery anode applications and identify its quantum confinement and its related effects on the electrochemical performance. GeO2 nanoparticles with different sizes of ∼ 2, ∼ 6, ∼ 10, and ∼ 35 nm were prepared by adjusting the reaction rate, controlling the reaction temperature and reactant concentration, and using different solvents. Among the different sizes of the GeO2 nanoparticles, the ∼ 6 nm sized GeO2 showed the best electrochemical performance. Unexpectedly smaller particles of the ∼ 2 nm sized GeO2 showed the inferior electrochemical performances compared to those of the ∼ 6 nm sized one. This was due to the low electrical conductivity of the ∼ 2 nm sized GeO2 caused by its quantum confinement effect, which is also related to the increase in the charge transfer resistance. Those characteristics of the smaller nanoparticles led to poor electrochemical performances, and their relationships were discussed.

Ultra-small, size-controlled Ni(OH)2 nanoparticles: elucidating the relationship between particle size and electrochemical performance for advanced energy storage devices

“…As seen in inset of Figure 3h, smaller Ni(OH) 2 nanoparticles have larger band gap values. Such a size-dependent blue shift in the band gap energy of the Ni(OH) 2 nanoparticles can be attributed to the quantum confinement effect, [10][11][12] which also has been observed in various semiconductor quantum dots or nanofilms, which include ZnO, 11 CdS, 25 CdSe 26 and InAs. 27 …”

“…Moreover, many works have proven that the conductivity of electrode materials is closely related to the diffusion of protons through the nanoparticle and the redox reaction rate on the surface. 10,13,[30][31][32][33][34][35] This result leads us to hypothesize that the charge transfer resistance (R ct ) and proton diffusion coefficient (D) in the electrodes and electrolytes could change and differ from the traditional understanding because the particle size of Ni(OH) 2 is less than the critical size.…”

“…It should be noted that the quantum confinement effect, a sort of nanosize effect, inevitably arises as the particle size reduces to the nanoscale, particularly when o10 nm. [10][11][12] Furthermore, we deduced the relationships between particle size, conductivity (σ) and ΔE (Equation (2) and Equation (3))…”

“…Importantly, most works have proved that σ is closely related to the ion diffusional limitation and the polarization loss for electrode materials, where a decrease in σ causes an inferior electrochemical performance of electrode materials. 10,[13][14][15][16] Inspired by the above analyses, we hypothesize that minimizing the particle size may have a negative effect on the electrochemical performance, such that a critical size should exist for electrode materials. In addition, while many nanomaterials used in electrochemical energy storage devices have been synthesized by various methods, a precisely size-controlled synthesis and a systematic study of size-dependent electrochemical performance for the electrode materials are rarely performed due to the difficulty in controlling the size, particularly when o10 nm.…”

High Energy Density Germanium Anodes for Next Generation Lithium Ion Batteries

“…They controlled the nanoparticle sizes by adjusting the reaction rate, reaction temperature and reactant concentration. Unexpectedly, particles smaller than 2 nm exhibited inferior electrochemical performance, arising from the low electrical conductivity due to quantum confinement effect and higher propensity to aggregate [53]. Contrary to the conventional notion that the smaller particles the better they are as anode materials, nanoparticles of diameters c.a.…”