Si-CNT/rGO nanoheterostructures as high-performance lithium-ion battery anodes

Sascha Dobrowolny, University of Duisburg-Essen, Duisburg, Germany
Lisong Xiao, University of Duisburg-Essen, Duisburg, Germany
Yee Hwa Sehlleier, University of Duisburg-Essen, Duisburg, Germany
Hans Orthner, University of Duisburg-Essen, Duisburg, Germany
Falko Mahlendorf, University of Duisburg-Essen, Duisburg, Germany
Hartmut Wiggers, University of Duisburg-Essen, Duisburg, Germany
Christof Schulz, University of Duisburg-Essen, Duisburg, Germany
Angelika Heinzel, University of Duisburg-Essen, Duisburg, Germany

Recently, rechargeable lithium-ion batteries (LIBs) have gained importance for electronic devices and electric vehicles. Thus, research and development focus on improving energy and power densities as well as durability of LIBs. Currently, commercially available graphite anodes with a specific capacity of 372 mAh g–1 are used but they cannot satisfy the abovementioned demands. Si is a very promising candidate as an anode material due to its high theoretical capacity of 3579 mAh g–1 at room temperature. However, this high specific capacity owing to host up to 3.75 Li atoms per Si atom leads to extreme volume expansion up to 300% during lithiation, which results in pulverization and delamination of the electrode material after few cycles.

ln this study, we propose a new strategy using reduced graphene oxide (rGO) in combination with a stabilized Si-CNT hybrid to generate a robust, highly conducting nanoheterostructure to further enhance the stability and the electrochemical performance of Si-based electrode materials. Si-Nanoparticles (Si-NP) were synthesized in the gas phase by decomposition of monosilane in a hot-wall reactor. Si-NPs and CNTs were functionalized and reacted to form Si-CNT hybrids, utilizing the formation of peptide bonds between amine-modified Si-NPs and the carboxyl-functionalized CNTs. The Si-CNT hybrids were then combined with GO by self-assembling to form a robust Si-CNT/rGO-composite. In this unique nanoheterostructure Si-NPs provide high capacity, rGO ensures high electrical conductivity for the entire structure and provides sufficient void spaces to buffer the volume changes of the Si-NPs, and CNTs act as the scaffolding to bind the Si-NPs and provide additional electrically-conductive channels.

Here, we present electrochemical investigations of Si-anodes based on Si-CNT/rGO composite material. The electrode preparation is based on a commercially established wet chemical doctor blade manufacturing process using a water based binder. The composite material shows a high reversible capacity of 1665 mAh g–1 with good capacity retention of 88.6% over 500 cycles when cycled at 0.5 C. The high-power capability is demonstrated at 10C (16.2 A g-1) where 755 mAh –1 are delivered, thus indicating promising characteristics of this material for high-performance LIBs.

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