Lithium-ion batteries have become the prevalent technology to power a variety of devices from portable electronics, through power tools to electric vehicles. Higher energy density batteries are desired for all this applications as they translate directly into reduced weight and/or increased autonomy. In this context, Lithium- and manganese-rich nickel-cobalt-manganese oxides (LMR-NMC) constitute a promising family of cathode materials that can deliver up to 250 mAh/g capacities, approximately twice the capacity of layered lithium metal oxides.

LMR-NMC materials can be considered as pseudobinary x Li₂MnO₃ · (1-x) LiMO₂ (with M a combination of Ni, Mn, and/or Co); i.e., metastable, mixed symmetry crystals containing regions of monoclinic Li₂MnO₃ topotaxially integrated into a layered LiMO₂ matrix. Li removal from the LMR-NMC cathode during battery operation destabilizes its crystal structure and causes cation rearrangement within the oxygen framework which results in a progressive descent of the battery operating voltage (hence, energy and power density) upon subsequent cycling. This phenomenon, known as Voltage Fade is a major contributor to performance decline over the lifetime of the battery.

In this talk, I will give an overview of the crystal structure transformations occurring during operation of lithium-ion batteries based on LMR-NMC cathodes and present recent progress toward understanding and controlling its impact on device properties.

Recently, as the environmental consciousness grows up, microbial fuel cell turns to rapidly develop because of its renewable and eco-friendly characteristics. Microbial fuel cell can perform wastewater treatment and produce electricity at the same time, and the factors to influence its efficiency are microbial inoculum, chemical substrate, operating configuration, proton exchange material, and electrode material. This study is divided into two parts, the first part is to conduct surface modification of anode material by thermal spraying Ni-graphite powder and nickel-copper alloy powder (mechanical alloying) respectively on 304 stainless steel to discuss the effect of power density for conductivity and corrosion resistance of metallic coating. The second part is development of cathode catalyst. Directly thermal spray nickel-copper alloy powder as the catalyst on carbon cloth to fabricate cathode and compare to non-catalyst cathode and nickel powder catalyst cathode. The catalyst properties are examined by oxygen reduction reaction (ORR) test. Finally, put anode and cathode into two-chamber MFC respectively, to analyze maximum power density output of the system. This work makes thermal spraying as the procedure for modifying electrode materials, and takes advantage of mass production property to reduce time and costs, looking forward to performing well on electricity generation for energy efficiency.

We have carried out investigations into the pseudo-capacitive energy storage potential of silver oxide thin film electrode materials prepared by reactive magnetron sputtering. The growth and morphology of the prepared films was investigated with the scanning electron microscope (SEM). The stoichiometry and oxidation states of the silver oxide films were monitored with x-ray diffraction (XRD), Raman spectroscopy, x-ray photoelectron spectroscopy (XPS) and Fourier transform infra-red spectroscopy (FTIR). Contact angle, contact angle hysteresis and surface energy measurements were used to investigate the penetration of the aqueous NaCl electrolyte into the porosities in the prepared silver oxide films. The effect of oxygen concentration on the electrochemical stability of the silver oxide films in aqueous NaCl electrolyte was investigated with open circuit potential (OCP) and Tafel plot measurements. The Faradaic redox reactions and the electrochemical double layer capacitance of the films when exposed to the NaCl electrolyte was monitored with cyclic voltammetry and electrochemical impedance spectroscopy (EIS) measurements using Nyquist plots. Our results indicate considerable promise for the electrochemical electrode energy storage application of silver oxide thin film electrode materials in specialised applications areas like aqueous marine environments.

TiO2 based materials are widely used in electrochemical cells due to its important properties such as suitable band gap and electron mobility, high surface area and chemical inertness. However, the fabrication of such devices, is often limited to substrate materials able to withstand the high temperatures associated with the semiconductor specific crystalline phases. Traditionally, substrates such as amorphous glass or single-crystal materials are used, however these materials are commonly associated with high production costs and their brittle or non-flexible nature further limits the development of flexible device applications. Polymer substrates on the other hand, are promising candidates towards low cost electronic device manufacturing.

In this work, direct writing of TiO2 based semiconducting inks through a nozzle-based robotic deposition on polymeric substrates, accompanied by low temperature post-processing and UV treatments is implemented as a novel approach for solar cell manufacturing, with high control over the deposited material dimensions and shape. In this study, we focus on the patterning of TiO2 based inks for low temperature processing of TiO2 crystalline / semi-crystalline films/patterns as the photoanode. The effect of the ink’s composition on the printing characteristics as well as the effect of the post-processing (temperature/UV treatments), on the electrical performance of the devices are both assessed. Furthermore, the relation between such performances and the obtained microstructure is discussed. The devices are mechanically characterized under cyclic stress conditions and the electrical performance of the tested devices is also monitored.

It is anticipated that direct writing represents a novel technique for layer-by-layer fabrication of µm-sized featured energy harvesting devices, with high potential for large-scale manufacturing under ambient-conditions.

Lithium-ion batteries (LIB), typically used to power portable electronic devices, are being explored for larger scale applications such as electric vehicles and energy storage for utility grids. To realize these types of applications, significant and simultaneous increase in energy density and cycle life is required. While silicon anode electrodes have a high specific capacity (~3500 mAh/g [1]), they suffer from limited cycling lives due to the large Si volume expansion during cycling as well as induced formation of solid electrolyte interphase (SEI) layers that inhibit Li ion diffusion [2]. Electrospinning Si nanoparticles within a conducting carbon-based fiber offers a way of obtaining high capacity with nanostructuring that can combat effects from Si volumetric changes. While the electrospun fiber mat anodes can have high capacities (>1000 mAh/g), they still suffer from capacity fade and SEI formation with cycling. Recently, a very thin Al₂O₃ layer was shown to be successful at preventing SEI formation on Si-based anodes [3]. Atomic layer deposition (ALD) is the preferred method to conformally coat complex, high surface area nanostructures with abrupt interfaces and angstrom-scale thickness control. Here the ability to conformally coat complex electrospun fiber mats with an ultrathin ALD Al₂O₃ layer is explored.

Samples from the same electrospun single-fiber mat were exposed to ten pulses of water, ozone or trimethylaluminum (TMA) prior to sequential ALD pulsing to elucidate the impact of initial pulse sequence’s ability to obtain high quality, conformal ~2 nm Al₂O₃ films on carbon-based fibers. To maintain fiber integrity, all films were deposited at 150°C using a thermal ALD process for 20 cycles. X-ray photoelectron spectroscopy (XPS) showed that the Al₂O₃ thickness on the fiber mat was dependent on initiation sequence, with TMA-initiated > ozone-initiate > water-initiated films. While this suggests that better nucleation may be achieved using initial TMA pulses, all three showed conformal, stoichiometric, pinhole-free films. Further, XPS showed that a carbon peak at ~283 eV associated with the fiber mat structure was removed with the ozone process which can alter the intrinsic properties of the fiber and subsequent performance. After 50 cycles in standard electrolyte, all Al₂O₃ coated mats retain interfiber porosity and suppress SEI formation which is known to cause capacity fade. The impact of initiation sequence as well as thickness on the electrical performance of the anodes will be discussed.

[1] T. Hatchard, J. Electrochem. Soc. 151 (2004) A838 [2] T. Hwang, NanoLett. 12 (2012) 802.

[3] H. Nguyen, J. Mat. Chem. 22 (2012) 24618.