Daniel Carriazo’s research while affiliated with Ikerbasque - Basque Foundation for Science and other places

The purpose of this perspective article is to showcase the different strategies followed in the last years for the integration of graphene into lithium–sulfur batteries. The article will also disclose the limitations and difficulties found out when trying to scale up graphene-based electrodes and their compatibility with novel electrolytes for the development of pre-industrial pouch cells operating under realistic conditions. Representative works and recent results on the use of graphene for Li-S batteries are included to provide context in the path carried out in the last years, underlining every step forward regarding the benefits of using graphene in this technology. Starting with the first graphene integration approaches within the sulfur-based electrodes, addressing the impact of chemical modifications, and going forward with the development of graphene-based binder-free self-standing aerogels and graphene-carbon composites with optimized performances at coin cell level, a complete evaluation of the different initial strategies is carried out. Further on, the efforts are focused on unraveling the synergistic effects of graphene-based electrodes with tuned electrolyte compositions, and finally the strategies to scale-up the systems to prototype pouch cells are also reviewed.

Now that fast action is needed to mitigate the effects of climate change, developing new technologies to reduce the worldwide carbon footprint is critical. Sodium ion capacitors can be a key enabler for widespread transport electrification or massive adoption of renewable technologies. However, a years‐long journey needs to be made from the first proof‐of‐concept report to a degree of maturity for technology transfer to the market. To shorten this path, this work gathers all the stakeholders involved in the technical development of the sodium ion capacitor technology, covering the whole value chain from academics (TRL 1–3) and research centers (TRL3–5) to companies and end‐users (TRL 6–9). A 360‐degree perspective is given on how to focus the research and technology development of sodium ion capacitors, or related electrochemical energy storage technologies, from understanding underlying operation mechanisms to setting up end‐user specifications and industrial requirements for materials and processes. This is done not only in terms of performance metrics, but mainly considering relevant practical parameters, i. e., processability, scalability, and cost, leading up to the final sustainability evaluation of the whole of the technology by Life Cycle Assessment (LCA) and Life Cycle Cost (LCC) analysis, which is of utmost importance for society and policymakers.

The development of alternative energy storage technologies such as sodium‐ion hybrid capacitors, which do not rely on critical raw materials such as cobalt or nickel, for the replacement of conventional lithium‐ion batteries for some niche applications, is extremely important to successfully achieve a sustainable development in our planet. In this work, we introduce a novel sodium‐ion hybrid capacitor system formed by the combination of an optimized nanostructured composite material containing reduced graphene oxide and tin pyrophosphate as negative electrode, and a high specific surface area graphene‐carbon composite as positive electrode. The electrochemical performance of each material has been individually evaluated using NaPF6 in EC/DMC as electrolyte, showing impressive specific capacity values above 100 mAh g⁻¹ at 2 A g⁻¹, for both faradaic and capacitive‐type electrodes. The integration of the electrodes in an optimized full cell with anode‐to‐cathode mass balance of 1.5 : 1, enabled stable full cells that can provide energy densities of almost 60 Wh kg⁻¹ at 3,000 W kg⁻¹, showcasing the potential of these type of materials in the design of next generation energy storage systems.

This work studies the use of epoxy and polyurethane formulations as binders for the aqueous processing of activated carbon (AC) electrodes used as positive and negative electrodes in Electrochemical Double Layer Capacitors (EDLCs). The use of amine and carbodiimide as crosslinkers is also evaluated. The mechanical properties of those different binders have been investigated, looking towards aqueous processable and flexible electrodes. Microstructural analysis of the fabricated AC electrodes has been carried out to understand the pore‐blocking effect exhibited by certain polymers. Furthermore, electrochemical characterization of all the systems has been performed by cyclic voltammetry, electrochemical impedance spectroscopy, and constant current charge/discharge measurements at different current densities. The obtained results show that polyurethane (PU) outperforms in terms of energy and power density the carboxymethyl cellulose:styrene butadiene rubber (CMC : SBR) reference system. Moreover, the studied polyurethanes maintain close to 100 % of their initial capacitance after 2500 cycles under a current density of 5 A g⁻¹ and a discharge time of 20 s.

Lithium-sulfur batteries (LSBs) have emerged as promising alternatives to replace Li-ion technology in lightweight applications, but they still face some important challenges that hinder their commercialization. To overcome them, several optimization strategies focusing on each battery component have been investigated. In this work, we have explored the symbiotic combination of an optimized high-sulfur loading graphene-containing cathode with a novel sparingly solvating electrolyte (SSE) consisting of 1,3-dioxolane (DOL) as solvent and 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether (OCTO) as diluent, at an E/S ratio of 7 μL mg−1. The impact of graphene incorporation into the cathode formulation and the physicochemical compatibility between cathode and electrolyte have been evaluated and compared to those obtained for the benchmarking DME/DOL electrolyte. Using the DOL/OCTO SSE enhanced wettability over our graphene-containing electrodes and hampered significant polysulfide dissolution. Most importantly, the electrochemistry of this system showed very promising values at coin cell level, achieving areal discharge capacities of 5.3 mAh cm−2 at C/10, enduring beyond 100 cycles with 65 % capacity retention. The transferability of the system to prototype cells was successfully demonstrated by assembling a monolayer pouch cell which reached initial capacities of 55 mAh and lasted more than 60 cycles, paving the way for real deployment and commercialization of this energy storage technology.

The development of the most promising next-generation Lisingle bondS batteries with an improved cyclability is one of the greatest challenges nowadays. In this sense, here, a novel imidazolium-based polymeric ionic liquid (PVI10Cl) was successfully synthesized and integrated into a high-performing sulfur cathode. The lithium polysulfide trapping ability of PVI10Cl was confirmed, which helps to accelerate conversion kinetics. This synergetic effect leads to enhanced C-rate response, improving the discharge capacities and reducing the overpotentials even at 1C in comparison with conventional PVdF binder. These features also allow cells to be operated for 100 cycles with excellent capacity retention. All in one, while conventional binders are viewed only as a “glue” to hold the active material together, it has been shown that PVI10Cl binder has additional functions and plays an active role during Lisingle bondS battery operation.

Proteins can be used as building blocks of functional materials for electrochemical applications due to their structural properties and the possibility to tailor their ionic and electronic conductive properties.[1] One of the most attractive applications is in the bioelectronics field, for example as energy storage devices such as Electrical Double Layer Capacitors (EDLCs), due to the nontoxicity and biocompatibility of the materials.[2] EDLCs are primarily used for applications where high power is required during a short period of time. They present several advantages, such as fast charge-discharge cycling, high power density, and outstanding long-term stability.[3] Traditionally, the incorporation of biomaterials in EDCLs is limited because they can be denaturalized in contact with organic solvents or salts. In addition, they easily interact with other cell components resulting in parasitic reactions and their complex purification processes hinder their commercialization.[4] These drawbacks can be overcome by introducing engineered proteins, since their amino acid sequences can be tuned resulting in 3D structures with varying degrees of complexity. Based on this approach, engineered proteins with improved conductivity will be introduced as interlayers with good stability and wettability, to ensure that the ions can shuttle freely between the two electrodes. In our case, consensus tetratricopeptide repeat (CTPR) proteins have been chosen [5] and engineered with the aim of increasing the ionic conductivity of the resulting variants. CTPR variants have been mixed with 5% PEG solutions and drop cast to obtain self-standing films. After being cross-linked, the films have been sandwiched in a two electrodes Swagelok-cell configuration between two electrodes made of activated carbon. KCl (3M) aqueous solution has been used as electrolyte for evaluating the electrochemical performance of the devices. The electrochemical characterization of the EDLC devices has been carried out using cyclic voltammetry (CV) and galvanostatic cycling (GC) to study the effect of the of the engineering strategy of the CTPR proteins on the EDLC performances. The CV curves of the devices using thin films of proteins with distinct mutations show quadratic capacitive responses for all the assembled EDLCs, demonstrating both its ability to isolate the two electrodes and to allow the diffusion of ions. The EDLCs capacitances were calculated and analyzed from the GC characteristics at different charge-discharge currents and compared with commercial glass fiber separators confirming their feasibility as safe and environmentally friendly separators. The ionic diffusive behavior of the devices has been also studied by electrochemical impedance spectroscopy (EIS). Finally, the effect of the thickness, porosity, polarity, wettability, and ionic conductivity of the different protein separators has been addressed to explore the role of the engineered proteins in EDLC devices. Acknowledgements This abstract is part of R&D&I project TED2021-131641B-C44, funded by MCIN/AEI/10.13039/501100011033 and by European Union NextGenerationEU/PRTR. This project has received funding from the European Union’s Horizon 2020 FET Open under the grant agreement No: 964593 References: [1] Ing, N.L., El-Naggar, M.Y. and Hochbaum., A.I, J. Phys. Chem. B. 2018, 122, 46, 10403–10423. [2] Mosa, I. M., Pattammattel, A., Kadimisetty, K., Pande, P., El-Kady, M. F., Bishop, G. W., Novak, M., Kaner, R. B., Basu, A. K., Kumar and C. V., Rusling, J. F., Adv. Energy Mater. 2017, 7, 1700358. [3] Jalal, N.I., Ibrahim, R.I. and Oudah, M.K., J. Phys.: Conf. Ser. 2021,1973,012015. [4] Wang, T., He, D., Yao, H., Guo, X., Sun, B. and Wang, G., Adv. Energy Mater. 2022, 12, 2202568. [5] Sanchez-deAlcazar, D., Romera, D., Castro-Smirnov, J., Sousaraei, A., Casado, S., Espasa, A., Morant-Miñana, M.C., Hernandez, J.J., Rodríguez, I., Costa, R.D., Cabanillas-Gonzalez, J., Martinez, R.V. and Cortajarena, A.L., Nanoscale Adv. , 2019,1, 3980-3991.

The growing requirements for electrified applications entail exploring alternative battery systems. Lithium‐sulfur batteries (LSBs) have emerged as a promising, cost‐effective, and sustainable solution; however, their practical commercialization is impeded by several intrinsic challenges. With the aim of surpassing these challenges, the implementation of a holistic LSB concept is proposed. To this end, the effectiveness of coupling a high‐performing 2D graphene‐based sulfur cathode with a well‐suited sparingly solvating electrolyte (SSE) is reported. The incorporation of bis(fluorosulfonyl)imide (LiFSI) salt to tune sulfolane and 1,1,2,2‐tetrafluoroethyl‐2,2,3,3‐tetrafluoropropylether based SSE enables the formation of a robust and compact lithium fluoride‐rich solid electrolyte interphase. Consequently, the lithium compatibility is improved, achieving a high Coulombic efficiency (CE) of 98.8% in the Li||Cu cells and enabling thin and dense lithium depositions. When combined with a high‐performing 2D graphene‐based sulfur cathode, a symbiotic effect is shown, leading to high discharge capacities, remarkable rate capability (2.5 mAh cm⁻² at C/2), enhanced cell stability, and wide temperature applicability. Furthermore, the scalability of this strategy is successfully demonstrated by assembling high‐performing monolayer prototype cells with a total capacity of 93 mAh, notable capacity retention of 70% after 100 cycles, and a high average CE of 99%.