Hybrid systems between batteries and supercapacitors are designed to bridge the gap between both technologies, developing high-power, high-energy, and long cycle life energy storage devices. Moreover, in the urgent need to transition to a more sustainable energy model, sodium-based chemistries are an excellent alternative to lithiumbased technologies. While various approaches have been tried in Na-ion capacitor (NIC) cell design, the upsidedown NIC configuration remains underexplored. This consists of using a Na-containing battery-type cathode instead of an anode, which eliminates problems such as the need for pre-sodiation or Na-plating. This setup also allows the electrolyte concentration to stay stable, with ions exhibiting a rocking-chair motion, ensuring stable ionic conductivity during cycling. However, the potential window of these systems can be limited by the formation of the SEI on the capacitive negative electrode. Therefore, the aim of this paper is to explore the limitations of activated carbon (AC) in upside-down NICs through ex-situ X-ray photoemission spectroscopy (XPS) characterization and comprehensive monitoring of the electrode under various full-cell conditions, thereby assessing how far this configuration can be pushed in terms of energy. The proposed system features a high-rate capability cathode, a Na3V2O2(PO4)2F/C composite prepared via a novel one-step microwave synthesis, which delivers 64 mAh g- 1 at 50C. The negative electrode employs a dried olive pits-derived AC with a surface area of 2138 m2 g- 1. Together, they enable a full cell achieving up to 69 Wh kg- 1 at 19 W kg- 1 and 29 Wh kg-1 at 4915 W kg- 1, with an impressive capacity retention of 74 % after 10,000 charge-discharge cycles.

Li-ion batteries employing graphite anodes have already reached their theoretical limit due to the low capacity of graphite. Nevertheless, alternate anodes using Li metal have gained rapid attention due to its high specific capacity though drawbacks include dendrite formation and surface passivation of the metal anodes. Herein, unlithiated graphite membranes have been employed as protective layers on the Li metal anodes to overcome the surface reaction on the Li metal in a Li/S cell. The diffusion of Li+ ions through the graphite protective layer has been studied using in situ and ex situ XRD and solid-state NMR technique to understand the feasibility of this concept and the diffusion mechanism in such systems.

Aqueous lithium-ion batteries (LiBs) have attracted considerable attention from academia and industry due to their inherent safety and sustainability, owing to the absence of flammable solvents. However, their practical implementation is limited by the narrow electrochemical stability window (ESW) imposed by water decomposition. To address this, we report the design and characterization of a series of urea derivative-based-aqueous-eutectic-electrolytes (UAEEs) composed of LiCl, LiClO 4 , urea, methylurea, dimethylurea, and water. Near-infrared-spectroscopy revealed that the incorporation of urea derivatives disrupts water–water hydrogen-bonding network, promoting the formation of smaller, more stable water clusters. The UAEEs demonstrated excellent physicochemical properties, including high thermal-stability (∼191 °C), remarkable ionic conductivity (∼27.6 mS cm −1 ), and an expanded ESW (∼4.47 V), which shows dependence on the component ratios. Density-Functional-Theory calculations supported these findings, indicating favorable HOMO–LUMO energy alignment and charge delocalization patterns that explain the enhanced oxidative and reductive stability of the system. Furthermore, half-cell studies using LiMn 2 O 4 (LMO) and Li 4 Ti 5 O 12 (LTO) electrodes confirmed the electrochemical compatibility of the optimized UAEEs, with LMO exhibiting fast redox kinetics and excellent cycling stability. Together, these results demonstrate that UAEEs effectively overcome the intrinsic ESW limitations of conventional aqueous-electrolytes, paving the way for their integration into next-generation safe and high-performance aqueous LIBs.

The structure and magnetic properties of P2-Na2/3Fe2/3Mn1/3O2 is resolved using operando diffraction and complimentary techniques, revealing how structural changes during (de-)sodiation differ with applied current density and contribute to capacity fading.

The effective flow of electrons through bulk electrodes is crucial for achieving high-performance batteries, although the poor conductivity of homocyclic sulfur molecules results in high barriers against the passage of electrons through electrode structures. This phenomenon causes incomplete reactions and the formation of metastable products. To enhance the performance of the electrode, it is important to place substitutable electrification units to accelerate the cleavage of sulfur molecules and increase the selectivity of stable products during charging and discharging. Herein, we develop a single-atom-charging strategy to address the electron transport issues in bulk sulfur electrodes. The establishment of the synergistic interaction between the adsorption model and electronic transfer helps us achieve a high level of selectivity towards the desirable short-chain sodium polysulfides during the practical battery test. These finding indicates that the atomic manganese sites have an enhanced ability to capture and donate electrons. Additionally, the charge transfer process facilitates the rearrangement of sodium ions, thereby accelerating the kinetics of the sodium ions through the electrostatic force. These combined effects improve pathway selectivity and conversion to stable products during the redox process, leading to superior electrochemical performance for room temperature sodium-sulfur batteries.

Room temperature sodium sulfur (RT Na-S) batteries with high theoretical energy density and low cost have recently gained extensive attention for potential large-scale energy storage applications. However, the shuttle effect of sodium polysulfides is still the main challenge that leads to poor cycling stability, which hinders the practical application of RT Na-S batteries. Herein, a multifunctional hybrid MXene interlayer is designed to stabilize the cycling performance of RT Na-S batteries. The hybrid MXene interlayer comprises a large-sized Ti3C2Tx nanosheets inner layer followed by a small-sized Mo2Ti2C3Tx nanoflake outer layer on the surface of the glass fiber (GF) separator. The large-sized Ti3C2Tx nanosheet inner layer provides an effective physical block and chemical confinement for the soluble polysulfides. The small-sized Mo2Ti2C3Tx outer layer offers an excellent polysulfide trapping capability and accelerates the reaction kinetics of polysulfide conversion, due to its superior electronic conductivity, large specific surface area, and Mo-rich catalytic surfaces. As a result, RT Na-S batteries with this hybrid MXene interlayer modified glass fiber separator deliver a stable cycling performance over 200 cycles at 1 C with an enhanced capacity retention of 71%. This unique structure design provides a novel strategy to develop 2D material-based functional interlayer for high-performance metal-sulfur batteries.

Rechargeable room-temperature sodium–sulfur (Na–S) and sodium–selenium (Na–Se) batteries are gaining extensive attention for potential large-scale energy storage applications owing to their low cost and high theoretical energy density. Optimization of electrode materials and investigation of mechanisms are essential to achieve high energy density and long-term cycling stability of Na–S(Se) batteries. Herein, we provide a comprehensive review of the recent progress in Na–S(Se) batteries. We elucidate the Na storage mechanisms and improvement strategies for battery performance. In particular, we discuss the advances in the development of battery components, including high-performance sulfur cathodes, optimized electrolytes, advanced Na metal anodes and modified separators. Combined with current research achievements, this review outlines remaining challenges and clear research directions for the future development of practical high-performance Na–S(Se) batteries. Graphic Abstract

Over the last years, hard carbon (HC) has been the most promising anode material for sodium-ion batteries due to its low voltage plateau, low cost and sustainability. In this study, biomass waste (spent coffee grounds, sunflower seed shells and rose stems) was investigated as potential material for hard carbon preparation combining a two-step method consisting of on hydrothermal carbonization (HTC), to remove the inorganic impurities and increase the carbon content, and a subsequent pyrolysis process. The use of HTC as pretreatment prior to pyrolysis improves the specific capacity in all the materials compared to the ones directly pyrolyzed by more than 100 % at high C-rates. The obtained capacity ranging between 210 and 280 mAh g-1 at C/15 is similar to the values reported in literature for biomass-based hard carbons. Overall, HC obtained from sunflower seed shell performs better than that obtained from the other precursors with an initial Coulombic efficiency (ICE) of 76 % and capacities of 120 mAh g-1 during 1000 cycles at C with a high capacity retention of 86-93 %.

Lithium iron phosphate (LiFePO4, LFP) is the most promising cathode material for use in safe electric vehicles (EVs), due to its long cycle stability, low cost, and low toxicity, but it suffers from low conductivity and ion diffusion. In this work, we present a simple method to obtain LFP/carbon (LFP/C) composites with different types of NC: cellulose nanocrystal (CNC) and cellulose nanofiber (CNF). Microwave-assisted hydrothermal synthesis was used to obtain LFP with nanocellulose inside the vessel, and the final LFP/C composite was achieved by heating the mixture under a N2 atmosphere. The resulting LFP/C indicated that the NC in the reaction medium not only acts as the reducing agent that aqueous iron solutions need (avoiding the use of other chemicals), but also as a stabiliser of the nanoparticles produced in the hydrothermal synthesis, obtaining fewer agglomerated particles compared to synthesis without NC. The sample with the best coating—and, therefore, the best electrochemical response—was the sample with 12.6% carbon derived from CNF in the composite instead of CNC, due to its homogeneous coating. The utilisation of CNF in the reaction medium could be a promising method to obtain LFP/C in a simple, rapid, and low-cost way, avoiding the waste of unnecessary chemicals.

P'2-Na0.67Mn0.67Ni0.33O2 (NMNO) is one of the most promising cathodic materials for new generation sodium-ion batteries (SIBs). One drawback that is preventing its commercialization is however the high instability in the potential window 2.5-4.5 V vs. Na+/Na, caused by degradation reactions affecting the material's structure and composition. Herein we propose a strategy to overcome this weak spot introducing the surface coating of the material particles with inert magnesium oxide, that has been chosen as coating agent because of its low molecular weight. This protective layer is able to reduce the structural instability of the material without modifying the mixed conduction properties and thus globally stabilizing the electrochemical performances. In fact, the electrode of NMNO coated with 7 % of MgO, after an initial stabilization, was able to deliver over 90 mAh g(-1) of reversible specific capacity at a current value of 50 mA g(-1), with a capacity retention of 70 % after 250 cycles, to be compared with the 30 mAh g-1 of the uncoated material. The effect of the coating on the particles surface is here investigated with differential electrochemical mass spectrometry, to analyze the influence of the treatment on the electrode/electrolyte interphase.

Transition metal (TM) layered oxides constitute a promising family of materials for use in Na-ion battery cathodes. Here O3-Na (Ni1/3Mn1/3Fe1/3) O2 was synthesised using optimised sol-gel and solid-state routes, and the physico- and electrochemical natures of the resulting materials were thoroughly studied. Significant differences in electrochemical behaviour were observed, and the use of in operando XRD determined this stemmed from the suppression of the P3 phase in the sol-gel material during cycling. This was attributable to differences in the degree of transition metal migration in the materials ensuing from the selection of synthetic route. This demonstrates that not only the choice of material, but also that of synthesis route, can have dramatic impact on the resulting structural and electrochemical nature, making such considerations critical in the future development of advanced Na-ion cathode materials.

Abstract In the last few decades, the use of iron oxide nanoparticles (IONPs) with magnetic properties, especially in biomedicine, has gained a great attention due to the wide range of applications of those systems in various fields. In the present work, iron oxide nanoparticles (IONPs) using β-cyclodextrin (β-CD) as capping agent were synthesized by normal co-precipitation and reverse co-precipitation methods. Syntheses were made at 25 kHz y 45 kHz and without ultrasound for both methods. As-synthetized IONPs were characterized using Fourier transform infrared spectroscopy (FT-IR), X-ray powder diffraction, thermal analysis, scanning electron microscopy, transmission electron microscopy, dynamic light scattering (DLS) and electrophoretic light scattering (z potentials). The analyses of vibration sample magnetometer confirmed that the nanoparticles have magnetic properties. Differences in particle size, organic coating degrees, and magnetization values for normal and reverse co-precipitation methods for obtained IONPs were observed. The particle size determined by Scherrer equation, SEM, TEM and DLS was increased at 45 kHz for both methodologies. The z potentials nearby ˗30 mV suggest that nanoparticles dispersion are moderately stable from aggregation. Potential use a platform for magnetic separation of IONPs modified with β-CD obtained by normal co-precipitation method in this work, are analyzed by FT-IR spectroscopy, using as a model IBF, taking in account the formation of inclusion complex between this molecule and the β-CD on the surface of IONPs.

Hard carbon is one of the most promising anode materials for sodium-ion batteries. In this work, new types of biomass-derived hard carbons were obtained through pyrolysis of different kinds of agro-industrial biowaste (corncob, apple pomace, olive mill solid waste, defatted grape seed and dried grape skin). Furthermore, the influence of pretreating the biowaste samples by hydrothermal carbonization and acid hydrolysis was also studied. Except for the olive mill solid waste, discharge capacities typical of biowaste-derived hard carbons were obtained in every case (≈300 mAh·g−1 at C/15). Furthermore, it seems that hydrothermal carbonization could improve the discharge capacity of biowaste samples derived from different nature at high cycling rates, which are the closest conditions to real applications.

The full commercialization of sodium‐ion batteries (SIBs) is still hindered by their lower electrochemical performance and higher cost ($ W−1 h−1) with respect to lithium‐ion batteries. Understanding the electrode–electrolyte interphase formation in both electrodes (anode and cathode) is crucial to increase the cell performance and, ultimately, reduce the cost. Herein, a step forward regarding the study of the cathode–electrolyte interphase (CEI) by means of X‐ray photoelectron spectroscopy (XPS) has been carried out by correlating the formation of the CEI on the P2‐Na0.67Mn0.8Ti0.2O2 layered oxide cathode with the cycling rate. The results reveal that the applied current density affects the concentration of the formed interphase species, as well as the thickness of CEI, but not its chemistry, indicating that the electrode–electrolyte interfacial reactivity is mainly driven by thermodynamic factors.

Ex situ X-ray absorption spectroscopy and in operando 57Fe-Mo??ssbauer 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-Mo??ssbauer 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

Rechargeable Li‐ion battery technology has progressed due to the development of a suitable combination of electroactive materials, binders, electrolytes, additives, and electrochemical cycling protocols that resulted in the formation of a stable electrode‐electrolyte interphase. It is expected that Na‐ion technology will attain a position comparable to Li‐ion batteries dependent on advancements in establishing a stable electrode‐electrolyte interphase. However, Li and Na are both alkali metals with similar characteristics, yet the physicochemical properties of these systems differ. For this reason, a detailed study on the electrode‐electrolyte interphase properties, composition, and structure is required to understand the factors that influence the battery's behavior. Herein, the research that has been performed on the electrode‐electrolyte interphase for both anode and cathode in the most important families of electrode materials, including carbonate ester‐based and advanced electrolytes such as ether‐based carbonates and ionic liquids is presented.

Nickel-rich LiNi0.8Mn0.1Co0.1O2 (NMC811) is one of the most promising Li-ion battery cathode materials and has attracted the interest of the automotive industry. Nevertheless, storage conditions can affect its properties and performance. In this work, both NMC811 powder and electrodes were storage-aged for one year under room conditions. The aged powder was used to prepare electrodes, and the performance of these two aged samples was compared with reference fresh NMC811 electrodes in full Li-ion coin cells using graphite as a negative electrode. The cells were subjected to electrochemical as well as ante- and postmortem characterization. The performance of the electrodes from aged NM811 was beyond expectations: the cycling performance was high, and the power capability was the highest among the samples analyzed. Materials characterization revealed modifications in the crystal structure and the surface layer of the NMC811 during the storage and electrode processing steps. Differences between aged and fresh electrodes were explained by the formation of a resistive layer at the surface of the former. However, the ageing of NMC811 powder was significantly mitigated during the electrode processing step. These novel results are of interest to cell manufacturers for the widespread implementation of NMC811 as a state-of-the-art cathode material in Li-ion batteries.

The use of two types of bulky cations, tetrabutylammonium (TBA(+)) and Cs+, as electrolyte additives in Na-O-2 batteries is investigated. These cations facilitate the stabilization of sodium superoxide in the electrolyte, promoting the solution-mediated pathway. Both the addition of TBA(+) and Cs+ favor the growth of larger NaO2 cubes than in the case of the electrolyte containing only sodium salt, particularly in the case of Cs+. In terms of full discharge capacity, both additives lead to an increase in the discharge capacity, which is greater in Cs+ (50% enhancement). TBA(+) also provides an improved stabilization of superoxide; nevertheless, the interaction is not as strong as in the case of Cs+ due to the steric hindrance set by the alkyl groups. The presence of these additives not only affects the NaO2 formation mechanism, but also influences the nature of the solid electrolyte interphase. The presence of Cs+ generates a more stable solid-electrolyte interphase, which increases the cycle life of Na-O-2 batteries. Overall, new insights are provided to control the growth of the discharge products, modify the oxygen reduction reaction mechanism, and protect the Na metal anode surface by adding bulky monovalent cations in the electrolyte formulation.

P2-Na 2/3 [Fe 1/2 Mn 1/2 ]O 2 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-Na 2/3 [Fe 1/2 Mn 1/2 ]O 2 half-cells operating in two different working voltage windows, one allowing and one preventing the high voltage phase transition occurring in P2-Na 2/3 [Fe 1/2 Mn 1/2 ]O 2 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-Na 2/3 [Fe 1/2 Mn 1/2 ]O 2 . 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-Na 2/3 [Fe 1/2 Mn 1/2 ]O 2 electrodes which is one of the causes of the observed capacity fading.

The P2/O3 layered oxide system is thought to benefit from a synergistic enhancement, resulting from the presence of both phases, which makes it a promising cathode material for Na-ion battery applications. Here, biphasic P2/O3-Na2/3Li0.18Mn0.8Fe0.2O2 is investigated via a combination of neutron and X-ray scattering techniques. Neutron diffraction data indicates that the O3 alkali metal site is fully occupied by Li. Real time operando X-ray diffraction data shows the structural evolution of the composite electrode - at the charged state there is no evidence of O2, OP4 or Z phases. The results presented herein provide new insight into site preference of Li in biphasic materials and highlights the value of utilizing multiple phases to achieve high performance layered cathode materials for sodium battery applications.