Assessing Charge Contribution from Thermally Treated Ni Foam as Current Collectors for Li-Ion Batteries

Abstract

In this report we have investigated the use of Ni foam substrates as anode current collectors for Li-ion batteries. As the majority of reports in the literature focus on hydrothermal formation of materials on Ni foam followed by a high temperature anneal/oxidation step, we probed the fundamental electrochemical responses of as received Ni foam substrates and those subjected to heating at 100 • C, 300 • C and 450 • C. Through cyclic voltammetry and galvanostatic testing, it is shown that the as received and 100 • C annealed Ni foam show negligible electrochemical activity. However, Ni foams heated to higher temperature showed substantial electrochemical contributions which may lead to inflated capacities and incorrect interpretations of CV responses for samples subjected to high temperature anneals. XRD, XPS and SEM analyses clearly illustrate that the formation of electrochemically active NiO nanoparticles on the surface of the foam is responsible for this behavior. To further investigate the contribution of the oxidized Ni foam to the overall electrochemical response, we formed Co 3 O 4 nanoflowers directly on Ni foam at 450 • C and showed that the resulting electrochemical response was dominated by NiO after the first 10 charge/discharge cycles. This report highlights the importance of assessing current collector activity for active materials grown on transition metal foam current collectors for Li-ion applications. Lithium-ion batteries have found widespread use in portable electronic devices due to their improved performance in comparison with other battery chemistries (e.g. lead-acid, NiMH etc.).1-4 Stimulated by the need for improved batteries for more demanding applications, the field has seen a wave of interest in the development of novel materials for every component of the battery (anode, cathode, current collectors and electrolytes).5-10 Practically all literature studies focused on the development of materials for Li-ion batteries report specific capacities primarily in terms of mAhg −1 . 11-13 While the use of common specific capacity units allows different material systems to be compared quickly, it often means that important considerations for real-world applications are ignored. For example, materials with low tap densities or a high degree of porosity can lead to electrodes which exhibit fantastic capacities in terms of mAhg −1 but poor mass loadings and thus areal/volumetric capacities which are unsuited to real-world devices. This is particularly true for nanoscale materials which often lead to sub-mg level electrode mass loadings. In fact, it is well established that materials tend to perform better when using low mass loadings, 14-17 making the concept of using low mass loadings particularly attractive in terms of maximizing the calculated capacity in terms of mAhg −1 . Given that the merits of materials are often assessed solely on the specific capacity (in terms of mAhg −1 ), it is crucial that the specific capacity values calculated for a system is a genuine representation of the material...

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