Investigation of Metal Oxide/Carbon Nanotubes as Anode Material for High Capacity Lithium-Ion Cells

With increasing demanding of energy, the development of advanced materials to improve battery performance has become increasingly important. Among the batteries on the forefront of the latest technologies, lithium-ion batteries (LIB) are the most popular rechargeable batteries systems. However, LIBs are reaching its limit in specific energy capability by the electrochemical materials used. For example, graphite, the current start-of-the-art anode in LIBs has a limited capability to store Li since the theoretical capacity of graphite is 372 mAh/g [1]. NASA is developing high energy and high performance lithium-ion (Li-ion) cell designs and batteries for future exploration mission under the NASA Space Power System project [2]. To meet NASA aerospace/space applications, rechargeable lithium-ion batteries with higher specific energy and energy density and improved safety are desired.

To achieve higher capacity and energy density, and to improve safety for current LIBs, the nanostructed metal oxide/carbon nanotubes (CNT) as an anode for the LIBs has been investigated. Metal oxides such as Fe₂O₃ are considered as promising anode active materials since Fe₂O₃ displays many attractive features such as high theoretical capacity (1007 mAh/g, which is ~ three times of that of graphite), safe, cost-effective, and environmentally friendly [3]. However, poor electronic conductivity of metal oxides and volume changes during the charge and discharge process results in rapid capacity fade of the metal oxide. CNTs are promising candidates also for use as anode material in lithium-ion batteries since CNTs possess unique structural, mechanical, and electrical properties. However, when CNTs are used alone as anode, they lack stable voltage performance and exhibit high irreversible capacity loss [4]. The nanostructured metal oxide on CNTs, with CNTs serving as backbone/host matrix in the anode, not only provides excellent electronic conductivity to overcome the low conductivity issue of metal oxides, but also acts as an effective buffering component for alleviating the degradation of structural integrity that results from the volume changes associate with the charging and discharging process. In addition, the CNTs are also part of active materials in the anode, resulting in additional capacity and improved energy density for the anode.

In this work, the metal oxide is uniformly attached to CNTs. The electrochemical properties of the developed metal oxide/CNTs as anodes in LIBs have been studied by various electrochemical techniques such as cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic/galvanodynamic techniques. Li-ion cells with metal oxides/CNT anodes and coupled with NASA advanced non-flammable electrolyte were constructed and cycled. The electrochemical constants, such as reversible capacity, irreversible capacity loss, and coulombic efficiency have been characterized. The rate capability and life cycling performance have been evaluated. The impact of electrolyte type and binder type on cycling performance has also been investigated. In addition, the lithiation/delithiation processes and possible mechanisms during the charge/discharge cycling of the developed metal oxide/CNTs anodes in LIBs have been investigated and will be discussed in this presentation.

References:

[1] Dahn J. R.; Zheng T.; Liu Y.; Xue J. S. Science 1995, 270, 590

[2] Mercer C. et al., “Energy Storage Technology Development for Space Exploration”, NASA/TM—2011-216964

[3] Brandt, A.; Balducci, A. J. Power Sources 2013, 230, 44-49.

[4] Casas C. d. l.; Li W. J. Power Sources 2012, 208, 74-85