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With the aim of achieving carbon neutrality, new policies to promote electric vehicle (EV) deployment have been announced in various countries. As EV sales gain market-share, the demand for batteries is growing very rapidly, and this has raised concerns about the raw-material supply. Therefore, efficient and environmentally friendly recycling methods for lithium-ion batteries (LIBs) are mandatory to properly implement circular economy paradigms in this field. Hydrometallurgical recycling methods are characterized by their selectivity, high product purity as well as low energy consumption. In order to accomplish a close-loop recycling method, in this work we propose the use of a deep eutectic solvent (DES) and alginate hydrogels as leaching reagent and adsorbent, respectively, for their reusability, availability and biodegradability. The solubility and thermal stability of a choline chloride-ethylene glycol based DES (choline chloride: ethylene glycol = 1:2) were investigated, 180 °C being regarded as the temperature threshold for this DES, and reaching up to 1.12 gCo L−1 solubility after 8 h leaching. Moreover, the DES can be reused after the eutectic state recreation with a performance over 80 % with respect to the pristine DES. Calcium cross-linked sodium alginate hydrogels, which were immersed in ethylene glycol and dehydrated afterwards, were able to extract cobalt from the leachate with an efficiency of 92 %. The aforementioned hydrogels can be reused after desorption and reach 91 % of the performance of the pristine ones. The DES together with alginate hydrogel brings therefore a highly efficient and reusable close-loop recycling method.

Sodium batteries are receiving increasing interest as an alternative to reduce dependence on lithium-based systems. Furthermore, the development of solid-state electrolytes will lead to higher-performing and safer devices. In this work, a Zn-based metal–organic framework (Zn-MOF-74) is combined as a physical barrier against the growth of dendrites, together with 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIm][TFSI]) ionic liquid, which provides improved mobility to sodium ions. It is demonstrated that the incorporation of the appropriate amount of ionic liquid within the pores of the MOF produces a considerable increase in ionic conductivity, achieving values as high as 5 × 10−4 S cm−1 at room temperature, in addition to an acceptable Na+ transference number. Furthermore, the developed Na[EMIm][TFSI]@Zn-MOF-74 hybrid solid electrolyte contributes to stable and dendrite-free sodium plating/stripping for more than 100 h. Finally, a more than notable extension of the electrochemical stability window of the electrolyte has been determined, being useful even above 7 V vs. Na+/Na. Overall, this work presents a suitable strategy for the next generation of solid-state sodium batteries.

Lithium-ion batteries (LIBs) have been gathering increasing attention worldwide as they are being widely used in portable devices and implemented in electric vehicles. With the increasing volume of LIBs poured into the market, the recycling of LIBs is becoming essential because the elements being currently used in LIBs, such as, Li and Co, have limited deposits in the world. In this paper, various recycling approaches, which are now prevalent or have the potential to become dominant in the near future are reviewed. Recycled materials reuse performance is included to exhibit the feasibility of these recycling technologies. Furthermore, emerging cathode chemistries are also introduced and possible recycling strategies for them are discussed.

Ex situ X-ray absorption spectroscopy and in operando 57Fe-Mössbauer spectroscopy measurements are conducted to examine in detail the ongoing reaction mechanism of potassium Prussian blue (K-PB) within the narrow [1.6–0.005 V] voltage range, and so to determine whether this material truly undergoes a conversion reaction, as we proposed elsewhere. The generation of Fe0 is confirmed by both techniques, finding that 40 to 58% of iron gets reduced to metallic iron at 5 mV. The elucidation of the mechanism by in situ 57Fe-Mössbauer spectroscopy further reveals a sequential process for the reduction (lithiation) of the two different iron species initially present in Prussian blue. Both high-spin Fe2+–N first and low-spin FeII–C next go through the unusual Fe1+/I formal oxidation state during the reduction process, before forming surface Fe0 nanoparticles (NPs) below 0.48 V. Upon charge, Fe0 NPs preferentially oxidizes into Fe+–N. Interestingly, these surprising Fe+ species play an important role in decreasing the overpotential during the charge (delithiation) process with respect to other conversion systems.

209 p., The electrochemical capacitors or supercapacitors are envisioned as potential next-generation energy storage systems because of their excellent storage capacity, power density, and long-term durability. However, all these advantages are overshadowed by their poor energy density. Thus, this thesis aims to achieve a high-energy supercapacitor device without compromising its power performance to make them more commercially viable for many applications. The research work is associated with the improvement of the supercapacitors in different device configurations, such as EDL, asymmetric, and hybrid LIC systems by integration of advanced material and cell design. The results obtained from the studies of different supercapacitor systems demonstrate that the variation in electrode mass, cell voltage, and electrolyte has a huge impact on the overall electrochemical performance, stability, life expectancy, and safety of the device. Therefore, careful optimization of cell design and advancement in electrode materials retains the high importance driving factors of the supercapacitors for the development of future energy storage technology.

Most lithium-ion capacitor (LIC) devices include graphite or non-porous hard carbon as negative electrode often failing when demanding high energy at high power densities. Herein, we introduce a new LIC formed by the assembly of polymer derived hollow carbon spheres (HCS) and a superactivated carbon (AC), as negative and positive electrodes, respectively. The hollow microstructure of HCS and the ultra large specific surface area of AC maximize lithium insertion/diffusion and ions adsorption in each of the electrodes, leading to individual remarkable capacity values and rate performances. To optimize the performance of the LIC not only in terms of energy and power densities but also from a stability point of view, a rigorous mass balance study is also performed. Optimized LIC, using a 2:1 negative to positive electrode mass ratio, shows very good reversibility within the operative voltage region of 1.5-4.2V and it is able to deliver a specific cell capacity of 28mAh(-1) even at a high current density of 10Ag(-1). This leads to an energy density of 68Wh kg(-1) at an extreme power density of 30kWkg(-1). Moreover, this LIC device shows an outstanding cyclability, retaining more than 92% of the initial capacity after 35,000 charge-discharge cycles.

[EUS] Manganeso dioxidozko superkondentsadore hibridoen karakterizazio elektrokimikoa, material aktiboen sintesi eta karakterizazio fisiko-kimikoa eta banakako elektrodoen ikerketa.

The last 10 years established the beginning of a post-lithium era in the field of energy storage, with the renaissance of Na-ion batteries (NIBs) as alternative for Li-based systems. The development of this technology has required intense work in materials research in order to produce and optimize anodes, cathodes, and electrolytes for NIBs. The strong and weak points of the main families of compounds for each battery component are analyzed in this progress report. Taking into account the achievements made in materials for NIBs, the industrial scene is analyzed through the existing prototypes and commercial cells and also from an economical viewpoint. In this scenario, where Na-ion technology seems to be ready for a coming second generation, the use of Na can be extended to almost the whole spectrum of electrochemical energy storage systems: the new room temperature Na-S systems, high-energy Na-air technology, or high-power Na-based hybrid supercapacitors. Thus, the degree of development of NIBs, together with the promising performance of newer Na-based energy storage systems, makes Na the key to the coming commercial post-lithium systems.

Herein we report a series of lithium ion capacitors (LICs) with extraordinary energy-to-power ratios based on olive pit recycled carbons and supported on graphene as a conducting matrix. LICs typically present limited energy densities at high power densities due to the sluggish kinetics of the battery-type electrode. To circumvent this limitation, the hard carbon (HC) was embedded in a reduced graphene oxide (rGO) matrix. The addition of rGO into the negative electrode not only forms a 3D interpenetrating carbon network but also wraps HC particles, facilitating ion diffusion and enhancing the electronic conductivity notably at high power densities. Electrochemical impedance spectroscopy (EIS) analysis reveals that charge-transfer resistance at electrode-electrolyte interphase and the charge-transport resistance within the electrode are considerably lower in the presence of rGO. In addition, charge-transport resistance remains constant upon cycling even at increasing current densities. Capacity gain at high current densities, owing to the reduction of the electrode resistance, triggers the overall LIC performance, allowing for the assembly of an ultrafast LIC delivering up to 200 Wh kg(AM)(-1) at low power rates and 100 Wh kg(AM)(-1). (C) The Author(s) 2019. Published by ECS.

The increasing complexity of portable electronics demands the development of energy storage devices with higher volumetric energy and power densities. In this work we report a simple strategy for the preparation of partially reduced graphene oxide/carbon nanotube composites (prGO–CNT) as highly packed self-standing binder-free films suitable as electrodes for supercapacitors. These carbon-based films are easily obtained by the hydrothermal treatment of an aqueous suspension of graphene oxide and CNTs at 210 °C and then compacted under pressure. The prGO–CNT films, which had an apparent density as high as 1.5 g cm−3, were investigated as binder-free electrodes for aqueous supercapacitors using 6 M KOH solution as the electrolyte. The results show that the presence of merely 2 wt% of CNTs produces a significant enhancement of the capacitance retention at high current densities compared to the CNT-free samples, and this improvement is especially relevant in systems formed using electrodes with high mass loadings. Volumetric capacitance values of 250 F cm−3 at 1 A g−1 with outstanding capacitance retention (200 F cm−3 at 10 A g−1) were achieved using the prGO–CNT electrodes with an areal mass loading above 12 mg cm−2.

The effort to increase the energy density of conventional electric double-layer capacitors (EDLCs) goes through the development of lithium-ion capacitors (LICs). Herein, we report a self-standing, binder-free composite as the battery-type negative electrode obtained by a low-cost and easily scalable method. Tin(IV) oxide nanoparticles (<10 nm) embedded in a reduced graphene oxide matrix (SnO2-rGO) were prepared by an in-situ synthetic approach that involves the freeze/freeze-drying of a graphene oxide suspension in the presence of a tin precursor and its subsequent thermal reduction under argon atmosphere. Physicochemical and electrochemical characterization confirmed the optimum nano-structuration of the composite showing ultrafast response at high current densities. Its coupling with a highly porous olive pits waste-derived activated carbon (AC) as the capacitor-type positive electrode, enables the fabrication of a LIC with an excellent energy density output. The newly designed LIC is able to deliver 60 Wh kg−1 at 2.9 kW kg−1 (tdischarge ≈ 1 min) and still 27 Wh kg−1 at 10.6 kW kg−1 (tdischarge ≈ 10 s).

Supercapacitors, also known as electrochemical capacitors, have witnessed a fast evolution in the recent years, but challenges remain. This review covers the fundamentals and state-of-the-art developments of supercapacitors. Conventional and novel electrode materials, including high surface area porous carbons for electrical double layer capacitors (EDLCs) and transition metal oxides, carbides, nitrides and their various nanocomposites for pseudocapacitors – are described. Latest characterization techniques help to better understand the charge storage mechanisms in such supercapacitors and recognize their current limitations, while recently proposed synthesis approaches enable various breakthroughs in this field.

Lan honetan superkondentsagailuen esparruan energia biltegiratzeko zenbait teknologiaren berri laburra emango dugu, beren funtzionamenduarekin batera. Hainbat superkondentsagailu motaren azterketa egin dugu, bai ikerketa, bai aplikazioen ikuspuntutik; gainera, aztergai hartuko ditugu konfigurazio bakoitzaren abantailak eta desabantailak eta propietateak, hala nola, gainazal azalera espezifikoa, kapazitantzia eta energia eta potentzia dentsitateak. Azkenik, CIC Energigunen superkondentsagailuen inguruan zenbait ikerketa lerrotan lortutako azken emaitzak aurkeztu ditugu.