Dr. Maider Zarrabeitia

The electrochemical properties of P2-Na2/3Mn0.8Fe0.1Ti0.1O2 layered oxide, which is a promising cathode material for rechargeable Na-ion batteries (NIBs), are evaluated with an optimized in-house ionic liquid (IL)-based electrolyte, and its performance is compared with that using carbonate-based electrolyte. The IL-based system reveals better electrochemical performance at room temperature than the carbonate electrolyte-based one at 0.1C and 1C, especially in terms of cycling stability, with a 97% capacity retention after 100 deep cycles (0.1C). The electrode/electrolyte interface is thoroughly studied in both systems by means of X-ray photoelectron spectroscopy and scanning electron microscopy so as proof that the formed interface is crucial to optimizing the electrochemical performance of NIBs. The carbonate-based system shows a thin, inhomogeneous, and unstable interface layer, while the IL-based one exhibits an even thinner but homogeneous and more stable interface, which may result in safer and longer-lasting NIBs. © 2019 American Chemical Society.

P2-Na2/3[Fe1/2Mn1/2]O2 layered oxide is a promising high energy density cathode material for sodium-ion batteries. However, one of its drawbacks is the poor long-term stability in the operating voltage window of 1.5–4.25 V vs Na+/Na that prevents its commercialization. In this work, additional light is shed on the origin of capacity fading, which has been analyzed using a combination of experimental techniques and theoretical methods. Electrochemical impedance spectroscopy has been performed on P2-Na2/3[Fe1/2Mn1/2]O2 half-cells operating in two different working voltage windows, one allowing and one preventing the high voltage phase transition occurring in P2-Na2/3[Fe1/2Mn1/2]O2 above 4.0 V vs Na+/Na; so as to unveil the transport properties at different states of charge and correlate them with the existing phases in P2-Na2/3[Fe1/2Mn1/2]O2. Supporting X-ray photoelectron spectroscopy experiments to elucidate the surface properties along with theoretical calculations have concluded that the formed electrode-electrolyte interphase is very thin and stable, mainly composed by inorganic species, and reveal that the structural phase transition at high voltage from P2- to “Z”/OP4-oxygen stacking is associated with a drastic increased in the bulk electronic resistance of P2-Na2/3[Fe1/2Mn1/2]O2 electrodes which is one of the causes of the observed capacity fading. © 2022, The Author(s).

Sodium-ion batteries (SIBs) are postulated as sustainable energy storage devices for light electromobility and stationary applications. The anode of choice in SIBs is hard carbon (HC) due to its electrochemical performance. Among different HC precursors, bio-waste resources have attracted significant attention due to their low-cost, abundance, and sustainability. Many bio-waste materials have been used as HC precursors, but they often require strong acids/bases for pre-/post-treatment for HC development. Here, the morphology, microstructure, and electrochemical performance of HCs synthesized from hazelnut shells subjected to different pre-treatments (i. e., no pre-treatment, acid treatment, and water washing) were compared. The impact on the electrochemical performance of sodium-ion cells and the cost-effectiveness were also investigated. The results revealed that hazelnut shell-derived HCs produced via simple water washing outperformed those obtained via other processing methods in terms of electrochemical performance and cost–ecological effectiveness of a sodium-ion battery pack. © 2022 The Authors. ChemSusChem published by Wiley-VCH GmbH.

In the pursuit of more affordable battery technologies, potassium-ion batteries (KIBs) have emerged as a promising alternative to lithium-ion systems, owing to the abundance and wide distribution of potassium resources. While chalcogenides are uncommon as intercalation cathodes in KIBs, this study’s electrochemical tests on CrSe2 revealed a reversible K+ intercalation/deintercalation process. The CrSe2 cathode achieved a KIB battery capacity of 125 mA h g−1 at a 0.1C rate within a practical 1-3.5 V vs. K+/K operation range, nearly matching the theoretical capacity of 127.7 mA h g−1. Notably, the battery retained 85% of its initial capacity at a high 1C rate, suggesting that CrSe2 is competitive for high-power applications with many current state-of-the-art cathodes. In-operando PXRD studies uncovered the nature of the intercalation behavior, revealing an initial biphasic region followed by a solid-solution formation during the potassium intercalation process. DFT calculations helped with the possible assignment of intermediate phase structures across the entire CrSe2-K1.0CrSe2 composition range, providing insights into the experimentally observed phase transformations. The results of this work underscore CrSe2’s potential as a high-performance cathode material for KIBs, offering valuable insights into the intercalation mechanisms of layered transition metal chalcogenides and paving the way for future advancements in optimizing KIB cathodes. © 2024 The Royal Society of Chemistry.

Exploring the next generation of batteries based on sustainable materials is crucial for transitioning to a post-lithium-technology era. Potassium-based technology is one of the candidates that could fulfil the sustainability criteria. The electrolyte plays a crucial role in battery performance, being responsible for ionic transport, cycling performance, working temperature, and safety. Polyethylene oxide (PEO)-based solid polymer electrolytes (SPEs) have been extensively studied. However, one of the drawbacks of SPEs is their poor ionic conductivity at room temperature (RT). Quasi-solid and solvent-free polymer electrolytes are a promising solution to this issue, combining the benefits of a liquid phase and SPEs. This work focuses on the development of cross-linked PEO, fluorinated K salt, and ionic liquid (IL)-based solvent-free SPEs for potassium batteries. The designed cross-linked ternary solvent-free SPEs are thoroughly characterized both physicochemically and electrochemically, achieving ionic conductivities of up to 1.6 × 10−3 S cm−1 at 20 °C. The solvent-free SPEs were tested in K cells at 20 °C, using a Prussian white (PW) cathode as a proof-of-concept. The effects that different fluorinated anions, such as bis(fluoromethanesulfonyl) imide (FSI−) and bis(trifluoromethanesulfonyl) imide (TFSI−), have on the electrochemical performance were analysed by investigating the solid electrolyte interphase (SEI) formed on the K metal surface through electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS) and magic-angle spinning solid-state nuclear magnetic resonance spectroscopy (MAS-ssNMR). © 2025 The Royal Society of Chemistry.