Wanjun Cao

A hybrid electrochemical device based on a synergetic inner combination of Li ion battery and Li ion capacitor for energy storage

Li ion battery (LIB) and electrochemical capacitor (EC) are considered as the most widely used energy storage systems (ESSs) because they can produce a high energy density or a high power density, but it is a huge challenge to achieve both the demands of a high energy density as well as a high power density on their own. A new hybrid Li ion capacitor (HyLIC), which combines the advantages of LIB and Li ion capacitor (LIC), is proposed. This device can successfully realize a potential match between LIB and LIC and can avoid the excessive depletion of electrolyte during the charge process. The galvanostatic charge-discharge cycling tests reveal that at low current, the HyLIC exhibits a high energy density, while at high current, it demonstrates a high power density. Ragone plot confirms that this device can make a synergetic balance between energy and power and achieve a highest energy density in the power density range of 80 to 300 W kg−1. The cycle life test proves that HyLIC exhibits a good cycle life and an excellent coulombic efficiency. The present study shows that HyLIC, which is capable of achieving a high energy density, a long cycle life and an excellent power density, has the potential to achieve the winning combination of a high energy and power density.

High performance of Li-ion capacitors and internal Li-ion capacitor/Li-ion battery hybrid cells

E technologies have been experiencing a recent renaissance in water treatment. These techniques are used for brackish desalination as well as in industrial applications. Examples of electrochemical separation processes include electrodialysis (ED) and capacitive deionization (CDI) and its advanced version, membrane CDI (MCDI). Very little is reported about the biofouling propensity of electrochemical treatment processes used for natural types of water. Adhered cells are not only likely to decrease the ion capacity of the electrical double layer, electrodes conductivity and transport properties of ion exchange membranes, but also as inactivated or dead cells they might present a beneficial substratum for the undesired attachment and proliferation of approaching planktonic bacteria. Surprisingly, only a few studies in the ED, CDI, and MCDI fields deal with the fundamental aspects of bacteria adherence to the electrodes and the development of biofilms under the influence of the electric fields prevailing in these installations. Most of the studies in this field refer to the problem from a sanitary point of view, preventing device-related infections in hospital environments or disinfecting contaminated liquids. The mechanisms of bacteria inactivation remained however rather speculative in most of the mentioned reports. The present study is focused on the factors governing bio-macromolecule and bacterial adherence and biofilm development on electronically conductive surfaces such as carbon, graphite and gold, as well as on ion exchange membranes, in the absence and the presence of an externally applied electric field. A two-electrode flow cell including one transparent (ITO) electrode for on-line microscopic observations is used for bacterial attachment and biofilm growth studies. The biofouled electrodes are analyzed for biovolume and live/dead bacteria by using confocal laser microscopy (CLSM). Quartz crystal microbalance with dissipation and electrochemical module (E-QCM-D) is used for studying mass and rate of electrosorption of model biomacromolecules and bacteria.Abstract: Oxidoreductase enzymes have been employed for almost 5 decades for energy conversion in the form of biofuel cells. However, most enzymatic biofuel cells in the literature utilize complex biofuels, but only partially oxidize the complex biofuel via the use of a single enzyme (i.e. glucose oxidase or glucose dehydrogenase). This presentation will detail the use of enzyme cascades at bioanodes for deep to complete oxidation of fuels to improve performance. These enzyme cascade will include natural metabolic pathways (i.e. the Krebs cycle), as well as minimal metabolic pathways to promote electron flux. It will also compare fuel options for biofuel cells and discuss the importance of structural orientation of enzymes and enzyme complexation in enzymatic cascades for efficient energy conversion. This enzyme cascades inspired us to consider mitochondria as bioelectrocatalysts as well, so direct mitochondrial bioelectrocatalysis will also be discussed.The electrooxidation of small organic molecules such as formaldehyde, formic acid, methanol, ethanol, ethylene glycol, glycerol, and so on is relevant to interconversion between chemical and electrical energies. Although these have considerably low thermodynamic potentials compared to hydrogen, the oxidation process generally demands high overpotentials because of the ubiquitous formation of surface‐blocking carbonaceous species. The occurrence of parallel pathways and the formation of stable soluble by‐products also contribute to the poor utilization of all electrons involved in the oxidation process. Thecomplex kinetics found in these systems can also result in nonlinear manifestations such as autocatalysis and oscillatory dynamics. Besides the considerable amount of earlier experimental reports, only recently has some understanding of the chemistry underlying the dynamics been achieved. Moreover, a number of interesting and unexpected behaviors have been observed under oscillatory regime. In this chapter, we briefly review the recent advances on the oscillatory electrooxidation of small organic molecules, with emphasis on (a) the general phenomenology, (b) the use ofin situ andonline approaches, (c) the effect of temperature, and (d) the oscillations on modified surfaces. Moreover, some implications of nonlinearities in low temperature fuel cells are also discussed.1 Universidade Federal do Rio de Janeiro, UFRJ Campus-Macaé Professor Aloísio Teixeira, Av. Aluizio da Silva Gomes, 50, Granja dos Cavaleiros, CEP: 27930-560, Macaé, RJ, Brazil. 2 Universidade Federal do Rio de Janeiro, Escola de Química, Departamento de Processos Inorgânicos, Av. Athos da Silveira Ramos, 149, Bloco E, Sl E-206 Ilha do Fundão, CEP: 21941-909, Rio de Janeiro, RJ, Brazil. * E-mail: rodrigosqm@macae.ufrj.brL cell operated with ionic liquid electrolytes is a very promising energy storage technology for electric vehicle and plug-in hybrid electric vehicle due to several favorable characteristics of ionic liquids. However, Li-air cells that employ room temperature ionic liquid (RTIL) electrolytes exhibit poor performance due to limited oxygen solubility and low reactant species mobility. To circumvent these aforementioned drawbacks, we investigated the electrical performance of a Li-air cell with ionic liquid electrolytes operating at high temperature. A continuum based model developed for ternary electrolyte system is used to quantify the performance of the Li-air cell, with an ionic liquid (MPPY-TFSI) electrolyte, as a function of operating temperature. Key parameters of ionic liquid electrolytes are obtained from atomistic simulations, such as molecular dynamics (MD) and density functional theory (DFT) calculations. The continuum based cell level simulation results show that the battery performance can be improved significantly by increasing operating temperature. For instance, specific capacity as high as 3000 mAh/g can be achieved at 110°C operating temperature, which is almost 25 times higher than its counterpart at room temperature. Simulation results also reveal that by increasing the operating temperature, the specific capacity can be improved significantly for high load current density, which is one of the most critical drawbacks in RTIL based Li-air battery. We also studied the effect of cathode thickness on the performance of Li-air battery at different operating temperature. The transport limitation of oxygen and lithium ions can be alleviated at higher operating temperature suggesting that even thicker cathode materials can be used to enhance the cell capacity at elevated temperature.

Investigation of Li‐Ion Capacitors' Cycle Performance

Li-ion capacitors were assembled with an activated carbon cathode and hard carbon/stabilized lithium metal powder (SLMP) anode. The stabilities of cathode and anode were determined by different methods, including the half-cell and full-cell methods. It was found that the highest potential of the activated carbon electrode should be less than 4.5 V vs. Li/Li+ potential; while the lowest potential of hard carbon/SLMP electrode should be greater than 0.1 V vs. Li/Li+ potential. Scanning electron microscopy images showed that the growth rate of the solid electrolyte interface (SEI) layer increased rapidly when the lowest potential of hard carbon/SLMP electrode was less than 0.1 V vs. Li/Li+ potential.