Sodium ion capacitors promise to serve high energy density at high power while eliminating dependence on critical raw materials such as lithium. However, several major challenges, such as the low first coulombic efficiency originated by the use of disordered carbon anodes, need to be addressed. One strategy to overcome this problem is to incorporate a pre-sodiation agent into the system to avoid depleting the ions from the electrolyte during the first cycles. Different pre-sodiation agents have been tested so far, however an ideal solution has not been developed yet. In the present study, the use of sodium mesoxalate is evaluated as it is a non-toxic, sustainable and commercially available compound. Sodium mesoxalate is incorporated in the formulation of the activated carbon positive electrode. Nonetheless, as it is not a straightforward addition, the formulation and fabrication process of the electrode is herein tailored to obtain a good dispersion of the salt alongside the electrode, ensuring its complete decomposition during the first cycles. The irreversible oxidation of the pre sodiation agent takes place at a potential of ca. 4.3 V vs. Na+/Na within a capacity output of 331 mAh g- 1 when integrated in an activated carbon towards its use as positive electrode in sodium ion capacitors technology.

Li-metal-based batteries are considered as the next alternative to Li-ion batteries owing to their high specific capacity and energy density. Alleviating the use of liquid electrolytes, solid-state batteries using polymer electrolytes have gained vast attention. However, Li-metal solid-state batteries have major concerns regarding the non-total suppression of dendrites and high reactivity of the Li metal with certain polymers like polycaprolactones and polycarbonates, having main chain ester groups and which are considered as alternatives to PEO-based matrices. Herein we have designed a robust polymer matrix, namely, poly(vinyl butyrate) ester starting from a biodegradable polymer that is highly stable with Li metal, with appreciable ionic conductivity and single-ion conducting properties. A first approach has been made on these types of polymer matrices that not only introduces a modified polymer architecture for dry ester-based electrolytes but also shows unprecedented improvement in electrolyte performance with Li-metal polymer batteries.

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.

Anode-less batteries have gained due attention, considering the easy industrial and safer processes involved. The initial absence of an anode ideally improves the gravimetric and volumetric capacity in a battery, and the assembly process is made easier with no handling of reactive metals. Sacrificial salts, on the other hand, have been shown to be feasible in general for batteries and supercapacitors as a solid electrolyte interphase (SEI) forming agent and supplying additional Li or Na to compensate for that spent in the building of SEI. Herein, for the first time, an in-depth analysis has been made on employing sacrificial salt as an effective component for anode-less systems. A clear understanding of the composition of the SEI, cathode electrolyte interphase (CEI), Li metal deposition, and homogeneity of the interphases has been studied to explore the numerous advantages that the sacrificial salts can offer.

Sodium-oxygen (Na-O2) batteries are a promising alternative for high-energy storage applications, but their practical use is limited by electrolyte instability and poor cycling performance. This study investigates the role of hindered glymes-ether-based solvents with bulky tert-butyl groups-in improving the electrochemical behaviour of Na-O2 batteries. We compare hindered glymes with conventional glymes in terms of discharge capacity, cycling stability, electrolyte interactions, and solid electrolyte interphase (SEI) composition. Although hindered glymes exhibit higher overpotentials, they outperform conventional glymes in cycle life. Post-mortem analysis confirms sodium superoxide (NaO2) as the primary discharge product, but hindered glymes promote a greater formation of hydrated sodium peroxide, likely due to differences in the exposed surface area of discharge products. Molecular dynamics simulations reveal that steric hindrance in hindered glymes weakens Na+-solvent interactions, facilitating Na+ desolvation, which improves cycling stability. This steric effect also reduces Na+ solvation, increases molecular rigidity, and limits discharge product stabilization, leading to higher polarization and smaller NaO2 cubes during discharge. However, the improved Na+ desolvation in hindered glymes enhances cycling performance, with hindered monoglyme (H-G1) showing a more pronounced effect due to its shorter chain. X-ray photoelectron spectroscopy (XPS) analysis demonstrates that weakened Na+-solvent interactions lead to a more inorganic SEI, which contributes to improved interfacial stability. These results position hindered glymes as a promising electrolyte solution for Na-O2 batteries, offering enhanced thermal and electrochemical stability while improving cycling performance.

Li6PS5Cl (LPSCl) argyrodites offer high room temperature ionic conductivity (>1 mS cm−1) and are among the most promising solid electrolytes. However, their chemical instability against Li metal compromises the long‐term cyclability. Using PEO‐LiTFSI as an interlayer or as a matrix for composite electrolytes is a promising strategy to address this issue. Nevertheless, the interphase of PEO‐LiTFSI and LPSCl requires further detailed investigations. This work explores the interfacial reactions between these phases using solid‐state nuclear magnetic resonance. Results show that PEO facilitates the formation of a complex with LiCl and Li3PS4 from LPSCl, resulting in an interphase material with limited local mobility, thus impeding ion transport. Although the addition of Br as a dopant can improve the ionic conductivity of LPSCl by inducing disorder and generating the Li vacancies, it makes the LPSCl more susceptible to PEO and increases the extent of the interfacial reaction. 6Li–6Li EXSY experiments demonstrate spontaneous Li‐ion exchange between the PEO and the LPSCl, yet this exchange is significantly hindered by reaction products within the PEO‐LPSCl interphase, attributable to their sluggish local dynamics. This study sheds light on the complex interfacial interaction between PEO‐LiTFSI and sulfide argyrodite, providing insights into designing solid electrolytes for the new generation of electrochemical devices.

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

Li7La3Zr2O12 (LLZO) garnets offering high ionic conductivity and electrochemical stability are among the most promising ceramic materials for lithium metal solid-state batteries. Although their application in composite polymer electrolytes (CPEs) with poly(ethylene oxide) (PEO) has been widely studied, their surface chemistry which is influenced by their hygroscopic nature is often neglected. This work reports on how the thermal treatment and the consequent elimination of secondary phases at the LLZO–PEO interface impacts the microstructure of the garnet-rich CPEs, which in turn affects their mechanical and ion-transport properties. It is shown that LLZO heat treatment restricts local polymer chain motions, indicating reinforcement of PEO/LLZO interactions which enhances the mechanical strength and homogeneity of the CPEs. These micro-scale modifications of CPEs eventually increase their ionic conductivity and improve the solid electrolyte/lithium metal interface. Thus, the Li+ exchange at the PEO/LLZO interface was studied by using 7Li–7Li exchange spectroscopy– nuclear magnetic resonance , and it was observed that after LLZO heat treatment, the interfacial Li+ exchange has significantly decreased, in line with a lower LiOH content. This result confirms the role of LiOH as an intermediate in the Li+ exchange reaction and that surface chemistry plays a more important role in the Li+ exchange than the local Li mobilities in the individual phases.

Heat treatment of LLZO garnets can effectively remove lithium hydroxide and carbonate layers from its surface, increase the Li dynamics in the structure and improve the processing of composite polymer electrolytes for solid-state batteries.

Phosphorylated cellulose nanofiber (CNF-P) is presented as novel and promising organic filler for the preparation of composite solid polymer electrolytes (SPE). The degree of phosphorylation was evaluated, and the CNF-P was characterized. The results show that the phosphorus incorporation promotes the flame-retardancy property of cellulose nanofiber. Solid polymer electrolytes were prepared using CNF-P and the poly(ethylene oxide) as a matrix and lithium bis(trifluoromethanesulfonyl)imide salt (LiTFSI), with a molar ratio of [EO]/[Li+] similar to 20. The incorporated CNF-P improved significantly the mechanical properties of the resulting SPE, especially its tensile strength reaching a value of 45 MPa. The resulting composite polymer electrolytes showed practical conductivity values exceeding 10(-4) S/cm at 70 degrees C and provide a wide electrochemical stability window above 5 V vs Li/Li+. Cycling performances of these composite SPEs have been evaluated in an all-solid-state battery half-cell configuration using Li metal anode and LiFePO4/C cathode showing the viability of such fillers in solid polymer electrolytes.

Li metal secondary batteries known for their high energy and power density are the much-awaited energy storage systems owing to the high specific capacity of Li metal. However, due to the instability of Li metal with common Li-ion battery electrolytes, a combination with a polymer electrolyte seems to be an effective strategy to alleviate the safety issues of employing Li metal and provide design conformity to the system. Current trends show improvements in different aspects, such as improving ionic conductivity, single-ion conductivity, mechanical stability, and electrochemical stability. A combination of all these properties has been a bottleneck for the development of polymer electrolytes for safe and efficient operation of all solid-state batteries. Herein, a multifunctional polysalt has been synthesized from green and sustainable materials, namely, ethyl cellulose, plasticized with adiponitrile, that contributes to meeting the critical properties enabling high compatibility with Li metal and a quasi-single-ion-conducting property while simultaneously acting as a matrix/filler for efficient operation of the cells. This multifunctional polymer matrix inhibits further decomposition of nitrile-based plasticizers on Li metal anodes with the formation of a favorable Li metal anode interface, thus enabling the utilization of high-voltage stable nitrile-based plasticizers (4.2 V) to be implemented as an electrolyte component for realization of high-voltage Li metal anode polymer batteries.

The incentives for the use of lithium metal negative electrode are easily justified considering the gain in energy density. Polymer electrolytes disclosed almost fifty years ago are still considered as an option for the most thought-for all solid-state systems. In fact, the only solid-state batteries commercialised are those from Blue Solutions® powering busses in Europe, using a Li° negative, a PEO [poly(ethylene oxide)] matrix with a LiTFSI solute and an LiFePO 4 cathode materials and operating at 70°C. 1500 -2000 cycles are routinely obtained. The main drawbacks of PEO, which is stable to lithium metal is a low conductivity at room temperature (10 -5 - 10 -6 Ohm -1 .cm -1 at 25°C) while it reaches easily 10 -3 - 10 -4 Ohm -1 .cm -1 at 70°C. The other impedimenta of PEO is the relatively low transference/transport number of the Li + cation (T + ≈ 0.2), resulting in the formation of a salt concentration gradient in the electrolyte upon operation, with concomitant polarisation and the triggering of dendrites when the Sand time is reached, shortening the cycle life-time. Other polymer matrices like poly(ε-caprolactone) PCL and poly(propylene carbonate) PPC show slightly better conductivity and higher transference number (T + ≈ 0.5), but are not stable in contact with lithium metal. Our strategy to increase the conductivity at lower temperature consisted in modifying the polymer architecture, from linear (PEO) to comb polymer in which medium length PEG segments (Mw 1000 - 2000) are attached to the main backbone via a flexible non-solvating tether (PPO). This optimises the speed of re-orientation of the solvating units, speed needed to favour the ionic motion. With these polymers and delocalised salts like LiTFSI or LiFSI, conductivities close to 10 -4 Ohm -1 .cm -1 at 25°C are obtained though with the same transference number as PEO. In order to improve the selectivity of the cation transport in PEs, it is necessary to immobilise the negative charges of the salt by attaching them to a polymer or nano-particles. The other option consists in modifying the salt architecture to slow down the diffusion/migration of the anions by increasing the interactions of the anions with themselves or with the polymer backbone. We have found that, starting for a simple cellulose derivative, the action of FSO 2 N=C=O results in the attachment of anions to the backbone and that the poly(salts) are now able to form an alloy with PEO or other poly(ethers), with excellent mechanical properties imparted by the rigid cellulose matrix, yet giving Li-only conductivities allowing battery operation. Alternatively, SiO 2 or Al 2 O 3 nano-particles can be grafted with delocalised anionic moieties, which result, when dispersed into PEO, in conducting composites with again excellent electrochemical and mechanical properties. Modification of the well-known anion TFSI to increase its interactions and slow it down have been undertaken: either hydrogen bonds, dipole interactions, chain entanglement, or π - π interactions have been introduced in the RSO 2 N (-) SO 2 CF 3 anion with R equal respectively CF 2 H—, (CH 3 ) 2 N—, (CH 3 OC 2 H 4 ) 2 N—, C 6 H 5 —. In all cases, higher T+ were obtained as compared with TFSI - , though the total conductivity was lower, but resulting still in σ Li + that translates into better lithium plating efficiencies as seen in the classical Li°/PE/Li° cycling tests and in batteries lifecycle. A final drawback of PEO is its inability to withstand voltages above 3.9 V vs. Li + :Li° while PPC for instance, stable to 4.5V, does decompose rapidly on the negative Li°. The obvious idea to combine a PEO based anolyte and a PPC catholyte stumbles on the consideration that PEO is far more solvating than PPC and deplete totally the polyester compartment, with no conductivity remaining. We solved this problem with the use of an immobilised polyanion in both the anolyte and catholyte, resulting in the stable operation of a Li°/NMC622 battery. All these research results will be discussed in details.

Battery energy storage plays a pivotal role in the current energy transition and sees an exponential growth. Excess energy produced in the grid and increasing renewable energy production requires efficient energy storage system to be developed. The development of such energy storage systems requires efficient materials screening, problem identification, and property evaluation. The behavior of new identified materials or the failure of existing material configuration needs effective analysis technique of which electrochemical impedance plays a major role. Herein, an effort has been made to estimate the extent of this technique in characterizing the different component of the battery namely anode, solid-electrolyte interface, cathode, cathode-electrolyte interface, and electrolyte materials. The failure analysis using electrochemical impedance spectroscopy has also been screened for battery components in liquid and solid-state battery configuration. The most pertinent materials and failure analysis have been identified with respect to the state-of-the-art to get a complete know-how of the versatility of the technique that could further help researchers to consider this technique for efficient screening of novel battery materials.

Solid state lithium metal batteries based on polymer electrolytes hold the most promising prospect to face energy density and safety issues encountered by conventional Li ion batteries. The use of two different polymers, one for the cathode and another one as electrolyte, brings a sufficient energy gap and chemical stability allowing compatibility with the positive electrode and lithium metal anode; thus, achieving remarkable benefits towards high-performance cells. The present work unveils the Li salt interdiffusion occurring between two different dual-ion conducting polymer electrolytes consisting of lithium bis(trifluoromethanesulfonyl)imide] (LiTFSI) dissolved in poly(ethylene oxide) (PEO) and poly(propylene carbonate) (PPC). Combining these polymers within the same device results in cell failure due to the migration of LiTFSI to the more solvating PEO. The replacement of LiTFSI by lithium poly[(4-styrenesulfonyl)(trifluoromethanesulfonyl)imide] (LiPSTFSI), in which the anion is immobilized at a polymeric backbone, proves to overcome salt migration between the polymer phases. LiFePO4 -based solid state lithium metal batteries using LiTFSI fail within the initial cycles, while cells with LiPSTFSI display an outstanding cycling performance, with above 80% capacity retention at C/10, over 120 cycles, and excellent coulombic efficiency of ca. 100%. The rational design and in-depth knowledge provided in this work are highlighted as key elements for the development of high-performance solid state lithium metal batteries.

Recycling lithium from spent batteries is challenging because of problems with poor purity and contamination. Here, we propose a green and sustainable lithium recovery strategy for spent batteries containing LiFePO 4 , LiCoO 2 , and LiNi 0.5 Co 0.2 Mn 0.3 O 2 electrodes. Our proposed configuration of “lithium-rich electrode || LLZTO@LiTFSI+P3HT || LiOH” system achieves double-side and roll-to-roll recycling of lithium-containing electrode without destroying its integrity. The LiTFSI+P3HT-modified LLZTO membrane also solves the H + /Li + exchange problem and realizes a waterproof protection of bare LLZTO in the aqueous working environment. On the basis of these advantages, our system shows high Li selectivity (97%) and excellent Faradaic efficiency (≥97%), achieving high-purity (99%) LiOH along with the production of H 2 . The Li extraction processes for spent LiFePO 4 , LiNi 0.5 Co 0.2 Mn 0.3 O 2 , and LiCoO 2 batteries is shown to be economically feasible. Therefore, this study provides a previously unexplored technology with low energy consumption as well as high economic and environmental benefits to realize sustainable lithium recycling from spent batteries.

Solid-state batteries are the holy grail for the next generation of automotive batteries. The development of solid-state batteries requires efficient electrolytes to improve the performance of the cells in terms of ionic conductivity, electrochemical stability, interfacial compatibility, and so on. These requirements call for the combined properties of ceramic and polymer electrolytes, making ceramic-rich polymer electrolytes a promising solution to be developed. Aligned with this aim, we have shown a surface modification of Ga substituted Li7La3Zr2O12 (LLZO), to be an essential strategy for the preparation of ceramic-rich electrolytes. Ceramic-rich polymer membranes with surface-modified LLZO show marked improvements in the performance, in terms of electrolyte physical and electrochemical properties, as well as coulombic efficiency, interfacial compatibility, and cyclability of solid-state cells.

Rechargeable alkali metal (i.e., lithium, sodium, potassium)‐based batteries are considered as vital energy storage technologies in modern society. However, the traditional liquid electrolytes applied in alkali metal‐based batteries mainly consist of thermally unstable salts and highly flammable organic solvents, which trigger numerous accidents related to fire, explosion, and leakage of toxic chemicals. Therefore, exploring non‐flammable electrolytes is of paramount importance for achieving safe batteries. Although replacing traditional liquid electrolytes with all‐solid‐state electrolytes is the ultimate way to solve the above safety issues, developing non‐flammable liquid electrolytes can more directly fulfill the current needs considering the low ionic conductivities and inferior interfacial properties of existing all‐solid‐state electrolytes. Moreover, the electrolyte leakage concern can be further resolved by gelling non‐flammable liquid electrolytes to obtain quasi‐solid electrolytes. Herein, a comprehensive review of the latest progress in emerging non‐flammable liquid electrolytes, including non‐flammable organic liquid electrolytes, aqueous electrolytes, and deep eutectic solvent‐based electrolytes is provided, and systematically introduce their flame‐retardant mechanisms and electrochemical behaviors in alkali metal‐based batteries. Then, the gelation techniques for preparing quasi‐solid electrolytes are also summarized. Finally, the remaining challenges and future perspectives are presented. It is anticipated that this review will promote a safety improvement of alkali metal‐based batteries.