Direct Growth of RuO2 Nano-Architectures on Current Collectors and Their Improved Performance in Lithium-Ion Batteries

Lithium-ion batteries have application in wide range of portable devices like cell phones, portable computers, camcorders, I-pods, peristaltic pumps, heart assist devices, oil and gas pipeline robots, seismic survey sensors, tactical communication radios and thermal imaging equipment, and satellite power sources.^1,2 They are now projected to automotive industry for electric vehicles (EV’s) and hybrid electric vehicles.³ The common electrode materials of conventional lithium ion batteries are graphite (anode), and LiCoO₂ or LiFePO₄ (cathode). They have certain limitations such as low capacities, safety issues and cost which hinder their applications.²

RuO₂ plays an important role in the family of metal oxides because of its interesting properties such as metallic conductivity, high chemical and thermal stability, catalytic activities, electrochemical redox properties, and field emitting behavior.⁴ It is one of the most successful electrode material for supercapacitors because of its wide potential window of highly reversible redox reactions, remarkably high specific capacitance, and a very long cycle life.⁵ In this material, conversion reaction using nanoparticles is also possible and high capacity of 1130 mAh g^-1, corresponds to the storage of 5.6 moles of Li ions per mole of RuO₂ and high coulombic efficiency (98%) has been observed.⁶But the material can withstand up to only three cycles due to a large volume expansion.

We have improved the cycle life performance of RuO₂ by directly depositing the material on stainless steel current collectors via low pressure chemical vapor deposition. RuO₂ nano-architectures were characterized by powder x-ray diffraction and field emission scanning electron microscope. Galvanostatic charge-discharge experiments were performed versus lithium metal in the voltage range 4 - 0.1V. As deposited RuO₂ nano-architectures were cycled well over 20 cycles at high capacity beyond the theoretical limit of 806 mAh g^-1(Fig. 1). The origin of the extra capacity will be discussed.

Acknowledgements: This work was supported by NSF PREM Award Number DMR-0934111 and NSF-EPSCoR Cooperative Agreement No EPS-1003897

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