• Energy Research

Abstract Biomass waste recently emerged as efficient precursors for hard carbon anode preparation for Na-ion batteries. Despite their very complex microstructure (organic/inorganic) there is a lack of knowledge about their impact on carbon formation. In this paper, the influence of inorganic impurities of three raw local biomass wastes (asparagus, grape and potato) on the hard carbon properties and on their electrochemical performance is investigated, by performing a washing step either before or after the thermal treatment (TT) at 1300 °C. When washing was done after the TT (with HCl), most of crystalline inorganic impurities (K, Ca, Si, Mg - based compounds) could be significantly removed. This triggered the increase of ultramicroporosity along with mesoporosity formation and graphite interlayer space (d002) contraction. Such observations are less pronounced on grape derived carbon due to the inorganic's catalytic induced local graphitization during pyrolysis. The oxygen content in the pristine carbons was high, owing to the presence of inorganic metal oxides and carbonates, and could be diminished after washing along with the amount of defects. Thus, the carbon content and the electronic conductivity of the materials were enhanced. The electrochemical performance improvement after washing was limited since the positive effect brought by impurities removal was negatively compensated by the changes occurring in the materials, particularly the increase in the specific surface area. Diffrently, the washing done before the TT (with water) induced only fewer changes on the materials porosity and structure and slightly improved capacity (from 215 to 230 mAh g−1). Furthermore, higher pyrolysis temperature (1400 °C) on washed HCs afforded a better reversible capacity up to 280 mAh g−1. This comprehensive study opens the door for green and mild synthesis approach to be further explored for sustainable fabrication of hard carbon for Na-ion batteries.

Lithium cation insertion and extraction in LiFePO4 were electrochemically studied with a cavity microelectrode (CME). Cyclic voltammetry measurements were used to characterize the kinetics of the material. LiFePO4 was successfully cycled from 0.1 mV s–1 up to 1 V s–1 and is therefore a suitable material to be used in high power applications, such as asymmetric hybrid supercapacitors. Several kinetic behaviors were observed depending on the sweep rate. The LiFePO4 was found to follow different kinetics behaviors depending of the sweep rate. The charge storage mechanisms were investigated for Liþ extraction/insertion.

Capacitive mixing (CapMix) and capacitive deionization (CDI) are currently developed as alternatives to membrane-based processes to harvest blue energy—from salinity gradients between river and sea water—and to desalinate water—using charge-discharge cycles of capacitors. Nanoporous electrodes increase the contact area with the electrolyte and hence, in principle, also the performance of the process. However, models to design and optimize devices should be used with caution when the size of the pores becomes comparable to that of ions and water molecules. Here, we address this issue by simulating realistic capacitors based on aqueous electrolytes and nanoporous carbide-derived carbon (CDC) electrodes, accounting for both their complex structure and their polarization by the electrolyte under applied voltage. We compute the capacitance for two salt concentrations and validate our simulations by comparison with cyclic voltammetry experiments. We discuss the predictions of Debye-Hückel and Poisson-Boltzmann theories, as well as modified Donnan models, and we show that the latter can be parametrized using the molecular simulation results at high concentration. This then allows us to extrapolate the capacitance and salt adsorption capacity at lower concentrations, which cannot be simulated, finding a reasonable agreement with the experimental capacitance. We analyze the solvation of ions and their confinement within the electrodes—microscopic properties that are much more difficult to obtain experimentally than the electrochemical response but very important to understand the mechanisms at play. We finally discuss the implications of our findings for CapMix and CDI, both from the modeling point of view and from the use of CDCs in these contexts.

An increasing demand on high energy and power systems has arisen not only with the development of electric vehicle (EV), hybrid electric vehicle (HEV), telecom, and mobile technologies, but also for specific applications such as powering of microelectronic systems. To power those microdevices, an extra variable is added to the equation: a limited footprint area. Three-dimensional (3D) microbatteries are a solution to combine high-density energy and power. In this work, we present the formation of Cu2Sb onto three-dimensionally architectured arrays of Cu current collectors. Sb electrodeposition conditions and annealing post treatment are discussed in light of their influence on the morphology and battery performances. An increase of cycling stability was observed when Sb was fully alloyed with the Cu current collector. A subsequent separator layer was added to the 3D electrode when optimized. Equivalent capacity values are measured for at least 20 cycles. Work is currently devoted to the identification of the causes of capacity fading.

Cobalt oxides have been extensively used as conductive additives for Ni-MH batteries. We report in this paper the performances of an original nanometric cobalt oxide, close to Co3O4, as electrode material for hybrid supercapacitors. This spinel type phase contains hydrogen, lithium, cobalt vacancies, and especially Co4þ ions within the structure, leading to a high electronic conductivity. Cyclic voltammetry and impedance spectroscopy measurements show interesting capacitance (320 F/g in 8M-KOH), as well as good electrochemical cycling with a small amount of carbon black (5%).

Monolithic porous carbon film has a great potential for integrated supercapacitors due to no polymer binder, reduced macropore volume, and good adhesion between current collector and active material. It is demonstrated that continuous carbide-derived carbon (CDC) films can be synthesized on various substrates by dry etching. CDC films show high volumetric capacitance of ∼180 F cm−3 in 1.5 M TEABF4/acetonitrile electrolyte.