Study of the Role of Void and Residual Silicon Dioxide on the Electrochemical Performance of Silicon Nanoparticles Encapsulated by Graphene.

Dimitrios-Panagiotis Argyropoulos,Filippos Farmakis,Panagiotis Giotakos,George Zardalidis,Maria Daletou

doi:10.3390/nano11112864

Dimitrios-Panagiotis Argyropoulos, Filippos Farmakis + Show 3 more

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https://doi.org/10.3390/nano11112864

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Abstract

Silicon nanoparticles are used to enhance the anode specific capacity for the lithium-ion cell technology. Due to the mechanical deficiencies of silicon during lithiation and delithiation, one of the many strategies that have been proposed consists of enwrapping the silicon nanoparticles with graphene and creating a void area between them so as to accommodate the large volume changes that occur in the silicon nanoparticle. This work aims to investigate the electrochemical performance and the associated kinetics of the hollow outer shell nanoparticles. To this end, we prepared hollow outer shell silicon nanoparticles (nps) enwrapped with graphene by using thermally grown silicon dioxide as a sacrificial layer, ball milling to enwrap silicon particles with graphene and hydro fluorine (HF) to etch the sacrificial SiO2 layer. In addition, in order to offer a wider vision on the electrochemical behavior of the hollow outer shell Si nps, we also prepared all the possible in-between process stages of nps and corresponding electrodes (i.e., bare Si nps, bare Si nps enwrapped with graphene, Si/SiO2 nps and Si/SiO2 nps enwrapped with graphene). The morphology of all particles revealed the existence of graphene encapsulation, void, and a residual layer of silicon dioxide depending on the process of each nanoparticle. Corresponding electrodes were prepared and studied in half cell configurations by means of galvanostatic cycling, cyclic voltammetry and electrochemical impedance spectroscopy. It was observed that nanoparticles encapsulated with graphene demonstrated high specific capacity but limited cycle life. In contrast, nanoparticles with void and/or SiO2 were able to deliver improved cycle life. It is suggested that the existence of the void and/or residual SiO2 layer limits the formation of rich LiXSi alloys in the core silicon nanoparticle, providing higher mechanical stability during the lithiation and delithiation processes.

Highlights

Lithium-ion Batteries (LIBs) are currently the most prominent choice for energy storage applications, especially for portable electronic devices, cordless power tools and electric vehicles thanks to their high energy density, long cycle life and low weight, compared to other energy storage technologies [1,2]
Nanostructured silicon nanoparticles encapsulated by graphene with a void space in between the Si core and the graphene shell were fabricated, using silicon dioxide as a sacrificial layer, which was removed with an hydro fluorine (HF) chemical etching treatment
The physical characterization via Transmission electron microscopy (TEM) and HRTEM demonstrated the evolution in the morphology of the active material, along the process stages from silicon nanoparticle to the final void containing nanostructures

Summary

Introduction

Lithium-ion Batteries (LIBs) are currently the most prominent choice for energy storage applications, especially for portable electronic devices, cordless power tools and electric vehicles thanks to their high energy density, long cycle life and low weight, compared to other energy storage technologies [1,2]. There is a continuous need to improve the overall electrochemical performance of lithium-ion batteries, as the constant technological advances in the fields of automotive industry and portable communication device industry demand higher specific energy and energy density (>400 Wh/kg and >800 Wh/L) [3] than commercially available cells. LIBs use graphite-based anodes (negative electrode), which have a capacity limitation due to the theoretical specific capacity of graphite versus Li/Li+ , ~372 mAh/g, Nanomaterials 2021, 11, 2864. The most promising material to replace graphite is silicon (Si) with a maximum specific capacity, at room temperature, of 3579 mAh/g at the lithiation phase of Li15 Si4 [5,6], offering, in addition, a low potential vs Li/Li+ , abundance, non-toxicity and huge know-how processing from the microelectronic industry. Pure silicon electrodes demonstrate a continuous capacity fading upon cycling leading to limited cell cycle life

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