Search

We investigate the impact of using a carbon based gas diffusion layer (GDL) as the current collector for Li-O2 batteries. It is shown that the GDL actively participates in ORR during discharge conditions and, if its mass is not accounted for, can lead to inflated discharge capacity figures compared to inert cathode supports. SEM and XRD analyses show that Li2O2 discharge products form on cathodes composed of as-received GDL in a similar manner to that observed for carbon on stainless steel (SS) current collectors (at applied currents of 100 μA cm−2 or less). The relative activity of the GDL, carbon on GDL and carbon-on-stainless steel current collectors from voltammetric measurements confirmed ORR and OER processes to be similar at all carbon-based surfaces. When heated above 300◦C, degradation of the binder in the GDL and associated loss of carbon from the substrate surface leads to reduced discharge times compared to the pristine GDL substrates. The data highlight the importance of the contribution to ORR/OER in carbon-based active current collector substrates when determining gravimetric capacities of Li-O2 batteries. © 2014 The Electrochemical Society. [DOI: 10.1149/2.0021414jes] All rights reserved.

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 Co3O4 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.

The contact geometry effect on anode-supported cells (ASCs) performances has been evaluated by means of current-voltage curves (I-V curves) and electrochemical impedance spectroscopy (EIS). The use of platinum meshes and Crofer 22 APU interconnects as current collectors has been compared. Additionally, the application of La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) as contacting paste between the electrode and the metallic current collector allowed to estimate its beneficial effect by enhancing the current distribution at the cathode side. An inverse proportionality between the ohmic contributions and the extension of the contacting area has been observed. The usage of a contacting layer positively affected the polarization contribution as well. Both effects influenced positively the cell performances. The reduction of the ohmic losses resulted in a higher impact on the power density.

The charging/discharging cycles, rate capabilities, cyclic voltammetry and electrochemical impedance spectra (EIS) of sol-gel prepared C-coated LiFePO4 (C-LFP-SG) and a commercial LiFePO4 (LFP-comm), in combination with two different current collectors, viz. Al foil and C-coated Al foil (Al-C) are studied. A flat voltage profile at ?3.4 V was seen during the charging/discharging cycle of C-LFP-SG/Al. However, C-LFP-SG/Al-C showed a continuous decrease in voltage during discharging and an increase during charging cycles. On contrary, LFP-comm/Al-C showed a constant flat voltage profile, whereas LFP-comm/Al shows a slight decrease during the discharge. C-LFP-SG/Al and LFP-comm/Al-C cells exhibit better electrochemical performance compared to C-LFP-SG/Al-C and LFP-comm/Al respectively. This is also reflected from a direct correlation between the flat potential behavior and their rate capabilities. From EIS measurements, we discuss the effect of C-coating on the charge-transfer resistances of LFP nanoparticles and current collectors. Raman analysis of carbon modes in all the cathodes and current collectors reveal that a large contribution from sp2 bonded carbon gives better electrochemical properties. Increasing sp3-like disordered carbon at the C-C interface leads to large polarization effects during the charging and discharging cycles. � 2015 Elsevier B.V. All rights reserved.

Mixed metal oxides designed by using 3d elements in the Periodic Table are expected to play pivotal role in energy storage. In this work, cetyltrimethyl ammonium bromide (CTAB) assisted hydrothermal homogeneous precipitation method and subsequent calcination are employed to synthesize festuca scoparia-like Ni0.3Co2.7O4 material and compared it with pristine spinel Co3O4 having ultralayered morphology. The specific capacitance (Cs) value for Co3O4 at 1 A g-1 current density is 202 F g-1 which has increased to 396 F g-1 for Ni0.3Co2.7O4 electrode. Further, we have taken two important factors into consideration in fabrication, (i) facile in situ fabrication method, and (ii) desired composition of the active oxide phase on a porous current collector. We have employed same hydrothermal method to grow Ni0.3Co2.7O4 precursor material in situ on Ni foam without using CTAB, and converted it into oxide by heat treatment. The in situ grown Ni0.3Co2.7O4 on Ni foam electrode shows the highest specific capacitance value of 1423 F g-1, which is 3.6 times larger than the value obtained using Ni0.3Co2.7O4 coated on Ni foil at 1 A g-1 current density, and excellent cycling stability up to 4000 cycles. The capacitance loss is only ?4% at 16 A g-1 and at 32 A g-1. This study confirms the influence of unique features such as current collector, composition, surface area, porosity, and microstructural properties of materials on their electrochemical performance. � 2015 Hydrogen Energy Publications, LLC.

Current lithium-ion battery anode research involves significant investigations of semiconducting materials, particularly Si as its theoretical specific capacity is >4000 mAh/g1. Previous theoretical studies showed that porous Si with a large pore size and high porosity can maintain its structure after Li ion induced alloying and swelling. Metal-assisted chemical (MAC) etching is shown here to form internally mesoporous nanowires in the form of a layer, etched from highly doped Si2-4. Some porous materials are well known to exhibit pseudocapacitive behaviour in aqueous electrolytes5,6. Maintaining the structure without stress-induced cracked caused by volumetric changes in material is crucial in achieving a high capacity and long cycle retention. Almost all investigations of nanoscale Si involve their deposition onto a metallic current collector electrode within the battery cell. Here, we demonstrate that pseudocapacitive behaviour can be harnessed when Si nanowires are etched to maximum mesoporosity, forming an electrically dead layer on silicon current collector electrodes. This limits insertion or alloying processes to form Li-Si phases7and charge is stored within the electric double layer, even in Li-ion containing electrolytes. Measurements using cyclic and linear voltammetry supported by Raman scattering spectroscopy and electron microscopy confirm surface charge storage mechanisms; pseudocapacitance is not observed when the same nanowires are used on stainless steel current collectors. In such cases, the rate of lithiation is shown to be related to the degree of porosity and the net surface electronic density of the porous silicon in accumulation mode during charging. References C. K. Chan, H. Peng, G. Liu, K. McIlwrath, X. F. Zhang, R. A. Huggins and Y. Cui, Nat. Nanotechnol. 3, 31 (2008). W. McSweeney, O. Lotty, N. Mogili, C. Glynn, H. Geaney, D. Tanner, J. Holmes and C. O'Dwyer, J. Appl. Phys. 114,034309 (2013). A. I. Hochbaum, D. Gargas, Y. J. Hwang, P. Yang, Nano Lett. 9, 3550 (2009). W. McSweeney, O. Lotty, J. D. Holmes and C. O'Dwyer, ECS Trans., 35, 25 (2011). P. Simon and Y. Gogotsi, Nat. Mater. 7, 845 (2008). T. Brezesinski, J. Wang, S. H. Tolbert and B. Dunn, Nat. Mater. 9, 146 (2010). W. McSweeney, O. Lotty, C. Glynn, H. Geaney, J. D. Holmes and C. O'Dwyer, Electrochim. Acta, 135, 356 (2014).