Oxygen-Functionalized Carbons for Rechargeable Lithium Batteries

Technology  

Sub-millimeter long few-walled carbon nanotubes (FWNTs) minimize the number of junctions, which can enhance electrical conductivity and the mechanical strength in self-standing networks. In the case of multi-walled carbon nanotube-graphene electrodes, multi-walled carbon nanotubes (MWNTs) can allow successful utilization of the high surface areas of graphene by serving as a “pillar” inserted between graphene sheets that helps reduce the extent of agglomeration, creating a novel ordered, hierarchical structure with electrochemically accessible surfaces. Oxygen functional groups of carbons have Faradaic reactions with lithium ions in lithium cells, therefore, the energy density of carbon electrodes can be controlled by the oxidation time. Functionalized MWNTs that include pseudo-capacitive functional groups are assembled using the layer-by-layer (LBL) technique. These additive-free LBL-MWNT electrodes exhibit high gravimetric energy (200 W h kgelectrode -1) delivered at an exceptionally high power of 100 kW kgelectrode-1 in Li/LBL-MWNT cells when normalized to the single-electrode weight, with no loss observed after completing thousands of cycles.   

Problem Addressed   

Batteries exhibit high energy as a result of faradaic reactions in the bulk of active particles, but are rate-limited. The alternative, electrochemical capacitors, can deliver high power but at the cost of low energy storage, by making use of surface ion adsorption (referred to as double-layer capacitance) and surface redox reactions (referred to as pseudo-capacitance). A promising approach to merging the advantages of these two different technologies is the use of nanostructured carbon electrodes. Nanostructured carbon electrodes use the faradaic reaction of the surface functional groups to store more energy than the double-layer capacitance on conventional capacitor electrodes and also provide high power capability.    

Advantages      

• Increases gravimetric energy
• Increases power delivery
• Increases cyclability  

Publications

"High-Power Lithium Batteries from Functionalized Carbon-Nanotube Electrodes." Nature, June 20, 2010.