The unique electronic, mechanical and thermal properties of graphene make graphene coated inorganic nanoparticles very promising materials for the future. These hybrid nanoparticles can be used in sensors, as fuel cell catalysts, in photovoltaics and optoelectronics, and also as material for high performance battery electrodes.
Electrochemically active metals and metal oxides such as Sn, Si, SnO2, Co3O4 are widely tested as anode materials for lithium ion batteries. As the host matrix of these materials exhibits a large specific volume change during the cycling process, a rapid electrode capacity decay is observed. To improve the cycle performance, carbonaceous materials with high electrical conductivity and fair ductility have been widely chosen as matrices for metals and metal oxides as they can effectively buffer the strain from the volume change of metal oxide during the charging-discharging processes and preserve the high electrical conductivity of the overall electrode. However, the metal and metal oxide nanoparticles are still prone to strong aggregation during the cycle processes.
We offer a new simple and low cost technology to fabricate graphene-encapsulated metal or metal compound nanoparticles. The resulting hybrid nanoparticles are protected by granted substance claims in US, CN and TW.
For example graphene-encapsulated metal oxides (GE-MO) are prepared by co-assembly between negatively charged graphene oxide and positively charged metal oxide nanoparticles.
Fig.1: Fabrication of graphene-encapsulated metal oxide (GE–MO) including 1) modification of the metal oxide by grafting aminopropyltrimethoxysilane (APS) to render the oxide surface positively charged; 2) hybrid assembly between positively charged oxide nanoparticles and negatively charged graphene oxide by electrostatic interactions; and 3) chemical reduction.
When used in battery electrodes, the unique GE-MO hybrid architecture exhibits different features such as suppression of aggregation of oxide nanoparticles, accommodation of volume change during the cycle process, leading to a rise to a high oxide content in the composite and maintenance of a high electrical conductivity of the overall electrode.
Fig. 2: Galvanostatic discharge–charge profiles of a) GE–Co3O4 and b) bare Co3O4 electrodes (current density=74 mAg-1).
Fig 2: Comparison of c) cycle performance of GE–Co3O4 (rectangle), mixed Co3O4/graphene composite (circle), and bare Co3O4 lectrodes (triangle) over 30 cycles, and d) cycle performance and Coulombic efficiency of the GE–Co3O4 electrode during 130 cycles (current density=74 mAg-1).
These results confirm that the proposed technology enables a good encapsulation of electrochemically active metal oxide nanoparticles by graphene sheets and results in materials with a remarkable lithium storage performance with high reversible capacity and excellent cycle performance.
K. Müllen, X. Feng, S. Ivanovici, S. Yang: "Fabrication of Graphene-Encapsulated Oxide Nanoparticles: Towards High-Performance Anode Materials for Lithium Storage.",
Angew. Chem. Int. Ed. 2010, 49, 8408–8411.
Highly cited paper with > 600 citations (source: web of science)
EP priority patent application filed 14.05.2010.
WO2011141486 and TW201206712 filed in 10.05.2011,
WO2011141486 nationalized in EP, US, JP, KR, CN.
US8611070, CN102917981B and TWI562898B patents granted.
EP notice of allowance 10.01.2017