The purpose of this study is to highlight the influence of some fabrication parameters, such as mass loading and porosity, which are not really elucidated and standardized during the realization of electrodes for supercapacitors, especially when using metal oxides as electrode materials. Electrode calendering, as one stage during the fabrication of electrodes, was carried out step-by-step on manganese dioxide electrodes to study the decreasing porosity effect on the electrochemical performance of a MnO₂ symmetric device. One other crucial parameter, the mass loading, which has to be understood and well used for realistic supercapacitors, was investigated concurrently. Gravimetric, areal and volumetric capacitances are highlighted, varying the porosity for low-, medium- and large-mass loading. Low-loading leads to the best specific capacitances but is not credible for realistic supercapacitors, except for microdevices. Down 50% porosities after calendering, capacitances are increased and become stable faster, suggesting a faster wettability of the dense electrodes by the electrolyte, especially for high-mass loading. EIS experiments performed on electrodes without and with calendering lead to a significant decrease of the device’s time response, especially at high loading. A high-mass loading device seems to work as a power battery, whereas electrode calendaring, which allows decreasing the time response, leads to an electrical behavior closer to that expected for a supercapacitor.

By selecting two electroactive species immobilized in a layered double hydroxide backbone (LDH) host, one able to act as a positive electrode material and the other as a negative one, it was possible to match their capacity to design an innovative energy storage device. Each electrode material is based on electroactive species, riboflavin phosphate (RF) on one side and ferrocene carboxylate (FCm) on the other, both interleaved into a layered double hydroxide (LDH) host structure to avoid any possible molecule migration and instability. The intercalation of the electroactive guest molecules is demonstrated by X-ray diffraction with the observation of an interlayer LDH spacing of about 2 nm in each case. When successfully hosted into LDH interlayer space, the electrochemical behavior of each hybrid assembly was scrutinized separately in aqueous electrolyte to characterize the redox reaction occurring upon cycling and found to be a rapid faradic type. Both electrode materials were placed face to face to achieve a new aqueous battery (16C rate) that provides a first cycle-capacity of about 7 mAh per gram of working electrode material LDH/FCm at 10 mV/s over a voltage window of 2.2 V in 1M sodium acetate, thus validating the hybrid LDH host approach on both electrode materials even if the cyclability of the assembly has not yet been met.

A Layered Double Hydroxide (LDH) compound LDH ([Mg₂Al(OH)₆]⁺ x 2 H₂O) intercalated with a redox active organic anion, Anthraquinone-2-sulfonate (AQS), has been envisioned as an electrode material for high power aqueous based battery. The purpose is to use this interlayer redox active molecule for the enhancement of the specific capacity at the LDH composite electrode, which should allow fast charge transfer at the negative electrode for high power storage applications. This is achieved by the reduction of AQS in charge and oxidation in discharge within a redox inactive LDH matrix. The first charge of this new material [Mg₂Al(OH)₆]⁺[AQSO₃]⁻ x 2 H₂O leads to a capacity of 100 mAh g⁻¹ at − 0.78 V vs Ag/AgCl (based on the weight of the active material) when operated in aqueous 1 M sodium acetate electrolyte. However, low cycling stability was observed, since a drastic loss in specific capacity occurs after the first charge. This study focuses at elucidating the mechanism behind this phenomenon via in situ UV/vis experiments. Subsequently, the dissolution of charged AQS anions into the electrolyte during the first charge of the anode has been identified and quantified. Such understanding of fading mechanism might lead to the design of improved LDH-based electrodes, which utilize redox active anions working in the positive potential range with enhanced cycling ability.

The electrochemical behavior of the lithium hexagonal tungsten bronze, Li_xWO₃, is investigated herein. The material was synthesized at a low temperature under hydrothermal conditions, yielding nanorod-like particles with growth along the c-axis. Upon cycling in a 5 M LiNO₃ aqueous electrolyte, a specific capacity of 71 C.g⁻¹ was obtained at 2 mV.s⁻¹, corresponding to a charge/discharge cycle of 10 min. The charge storage mechanism was elucidated using various complementary techniques, such as electrochemical quartz crystal microbalance (EQCM) and synchrotron operando X-ray absorption spectroscopy (XAS). A desolvation process upon Li⁺ intercalation into the lattice of the material was evidenced, accompanied by a reversible reduction/oxidation of tungsten cations in the crystal structure upon charge/discharge cycling.