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Composite polymer electrolytes are systems of choice for future solid-state lithium metal batteries (LMBs). Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) is among the most interesting matrices to develop new generation quasi-solid electrolytes (QSEs). Here it is reported on nanocomposites made of PVDF-HFP and pegylated SiO2 nanoparticles. Silica-based hybrid nanofillers are obtained by grafting chains of poly(ethylene glycol) methyl ether (PEG) with different molecular weight on the surface of silica nanoparticles. The functionalized nanofiller improves the mechanical, transport and electrochemical properties of the QSEs, which show good ionic conductivity values and high resistance against dendrite penetration, ensuring boosted long and safe device operation. The most promising result is obtained by dispersing 5 wt% of SiO2 functionalized with short PEG chains (PEG750, Mw = 750 g mol−1) in the PVDF-HFP matrix with an ease solvent-casting procedure. It shows ionic conductivity of 0.1 mS cm−1 at 25 °C, more than 250 h resistance to stripping/plating, and impressive results during cycling tests in LMB with LiFePO4 cathode.

Complete decarbonization of hard-to-abate industrial sectors is critical to reach the carbon neutrality goal set for 2050. The production of nitrogen-containing fertilizers (N-fertilizers) is responsible for 2.1% of the overall global carbon dioxide emissions. Urea is the most common N-fertilizer, and it is currently produced through the Bosch-Meiser process starting from ammonia (NH3) and carbon dioxide (CO2). Electrochemical production of urea can reduce drastically the emission of greenhouse gases and the energy required for the process. Promising results were recently reported using nitrate (NO3−) and CO2 as reagents with increasing production rate and faradaic efficiency. In this mini-review, we summarize the most recent studies, including reaction mechanisms, electrocatalysts, and detection methods, highlighting the challenges in the field. A roadmap for future developments is envisioned with the scope of reaching industrial requirements.

It is vital to comprehend the charge/discharge behaviors of batteries to improve their properties. In this paper, we normalize the electrode materials’ behaviors according to the time of the process to allow a rational comparison between different materials and batteries.

The sodium-ion battery (Na-ion battery, NIB) is considered the most promising post-lithium energy storage technology, taking advantage of using the same manufacturing technology as Li-ion batteries (LIBs), while enabling the use of more abundant and economic, thus more sustainable, raw materials. Due to the inability of Na+ ions to be intercalated within the graphene-layered structure of graphite-based electrodes (the state of art anode material in LIBs), highly disordered and microporous carbons, known as hard carbons, are considered the anode material of choice for NIB technology. Biomass-derived biochar (BC) is one of the most relevant classes of hard carbons, exhibiting a good combination of sustainable fabrication, structural-morphological features and electrochemical performances. In this review, the main achievements on BC are rigorously reported from the production to the application into NIBs, with particular emphasis on the strategies to improve the electrochemical behaviour of BC by activating it and tailoring its chemical and structural properties. These strategies include selecting specific feedstocks, modulation of the pyrolysis temperature, pre- and post-production treatments, and materials engineering. The possible role of BC in sustainable NIBs development is also briefly discussed, together with some insights of its use in other post-Li energy storage systems and some concluding remarks and future direction of the research.

The penetration of Li-ion batteries (LIBs) in the automotive market makes a zero-waste vision for battery recycling urgent. This can play a crucial role in developing a circular economy through the recovery of critical raw materials (CRMs) as well as bringing non-metallic components back to use. In recent years, recycling technologies for LIBs entered a new stage focused on the development of advanced pre-treatment processes to separate all the valuable battery components and more sustainable metallurgical approaches. Compared to common recycling processes, supercritical fluid (SCF) technology has great advantages related to its environmental benignity; chiefly, if CO2 is used as the SCF (scCO2), it is an outstanding solvent for green chemistry approaches. This review aims at providing an overview on the current progresses and open challenges of SCF technology for the treatment of end-of-life LIBs. The fundamentals of SCF technology process are discussed, providing the reader a brief overview of principles, operation procedures and instrumentation. Thereafter, the main applications in the field of battery recycling are reviewed. Successful methods for battery electrolyte recovery via scCO2 are discussed together with pioneering studies on the extraction of critical metals from the cathode that demonstrate promising recovery rates (>60%) for Li, Co, Mn, and Ni. Finally, a specific focus is given on the huge innovation potential of scCO2 to separate and reuse the fluorinated binder from the electrode. At present, the binder is burnt in common recycling processes, leading to hazardous fluorinated gas emissions. This review aims to emphasize the opportunities of the SCF technology in battery waste treatment as a promising approach for resource recovery with significant economy and environmental perspectives.

ithium-ion batteries (LIBs) are at the forefront of electrochemical energy storage both for consumer electronics, and for power/energy more demanding applications, such as in automotive and grid levelling. However, their chemical and electrochemical stability must be further improved. Among the instability causes, a major role is played by residual moisture. As a matter of fact, hydrofluoric acid generated by hydrolysis of LiPF6, the most common lithium salt in LIBs, causes safety issues and performance losses. Here we demonstrate the scavenging properties vs. HF of a barium silicate glass used as a filler in a PVDF-HFP based gel polymer electrolyte. A full LiTi2(PO4)3|electrolyte|LiMn2O4 cell is stable for 200 cycles at 0.1C.

New generation lithium batteries require better performances, improved safety, and sustainability. Better performances can be obtained with lithium anodes and high-voltage cathodes, which in turn pose more pressure on the electrolyte stability, which is mandatory for safety. Deep Eutectic Solvents (DESs) are promising components for safer and more environmentally sustainable electrolytes. We investigate the physico-chemical properties of DESs made with 2,2,2-trifluoroacetamide (TFA) and LiPF6. The best composition is tested against Li metal and two cathode active materials: LiFePO4 (LFP) and high voltage LiNi1-x-yMnxCoyO2 (NMC). We obtain good electrochemical performance in a Li-metal cell with LFP. Accelerated rate calorimetry shows improved thermal stability of the Li|DES|NMC cell with respect to a commercial liquid electrolyte.

As highlighted by the recent roadmaps from the European Union and the United States, water electrolysis is the most valuable high-intensity technology for producing green hydrogen. Currently, two commercial low-temperature water electrolyzer technologies exist: alkaline water electrolyzer (A-WE) and proton-exchange membrane water electrolyzer (PEM-WE). However, both have major drawbacks. A-WE shows low productivity and efficiency, while PEM-WE uses a significant amount of critical raw materials. Lately, the use of anion-exchange membrane water electrolyzers (AEM-WE) has been proposed to overcome the limitations of the current commercial systems. AEM-WE could become the cornerstone to achieve an intense, safe, and resilient green hydrogen production to fulfill the hydrogen targets to achieve the 2050 decarbonization goals. Here, the status of AEM-WE development is discussed, with a focus on the most critical aspects for research and highlighting the potential routes for overcoming the remaining issues. The Review closes with the future perspective on the AEM-WE research indicating the targets to be achieved.

Hybrid silica-based nanofillers were synthesised by grafting short chains of poly(ethylene glycol) (PEG) with different molecular weight on the surface of SiO2 porous nanoparticles. Based on this approach, homogeneous poly(ethylene oxide) (PEO)-based ceramic-in-polymer solid-state electrolytes with SiO2 loadings up to 23 wt% were obtained, thanks to the high compatibility between the two phases endowed by the grafted PEG chains. These electrolytes showed satisfying ionic conductivity and excellent resistance against dendrite piercing that enabled long operation, for more than 350 h, under continuous stripping/plating of lithium in symmetric Li/electrolyte/Li cells. Additionally, the operating life of these devices was improved by the self-healing reaction between Li dendrites and silica fillers, being able to reinstate the cycling after short circuit. Finally, a lithium metal full cell, equipped with LiFePO4 positive material and the solid-state electrolyte containing 18 wt% of SiO2, demonstrated high stability against dendrite penetration and discharge capacity at 70 °C comparable to cells based on liquid analogues.

The transition to a circular economy vision must handle the increasing request of metals required to satisfy the battery industry; this can be obtained by recycling and feeding back secondary raw materials recovered through proper waste management. Here, a novel and green proof-of-concept was developed, based on deep eutectic solvents (DESs) to fully and easily recover valuable metals from various cathode active materials, including LiMn2O4, LiNi0.5Mn1.5O4, and LiNi0.8Co0.2O2. DES composed of choline chloride and lactic acid could leach Li, Mn, Co, and Ni, achieving efficiency of 100 % under much milder conditions with respect to the previous literature. For the first time, to our best knowledge, a two-step approach was reported in the case of LiNi0.8Co0.2O2 for selective recovery of Li, Co, and Ni with high yield and purity. Furthermore, other cathode components, namely aluminum current collector and binder, were found to be not dissolved by the proposed DES, thus making a simple separation from the active material possible. Finally, this strategy was designed to easily regenerate and reuse the leaching solvents for more than one extraction, thus further boosting process sustainability.

Pyrophosphates of the general formula A2BP2O7 (A = alkali metal and B = transition metal) find applications in several technological fields, including rechargeable Na-ion batteries. They present a rich polymorphism vs composition, which may strongly influence their functional properties. Therefore, to selectively obtain a specific structure is crucial for applications. Here, we combine structural investigation techniques (solid-state NMR, X-ray and neutron diffraction, and DFT calculations) to investigate the crystal chemistry of the series Na2(M/M’)P2O7 with couples M/M’ = Co/Zn and Co/Fe. For both the series, a phase transition vs composition is observed. A tetragonal to orthorhombic phase transition is found for the Zn/Co series, and an orthorhombic to triclinic phase transition is found for the Co/Fe series. Such changes are interpreted in view of the different electronic structures of the transition metal ion. In addition, with the support of modeling, short- and long-range structural analysis, we show that the coexistence of two polymorphs for a given composition is possible, suggesting that the final structures may be strongly dependent upon the synthesis procedure.

Batteries based on organic electrolytes have been raising safety concerns due to some associated fire/explosion accidents caused by the unusual combination of highly flammable organic electrolytes and high energy electrodes. Nonflammable aqueous batteries are a good alternative to the current energy storage systems. However, what makes aqueous batteries safe and viable turns out to be their main weakness, since water molecules are prone to decomposition because of a narrow electrochemical stability window (ESW). In this perspective we introduce aqueous batteries and then discuss the state-of-the-art of water-in-salt (WIS) electrolytes for aqueous energy storage systems. The main strategies to improve ESW are reviewed, including: (i) the use of fluorinated salts to make a solid electrolyte interphase (SEI); (ii) the use of cost-effective and highly soluble salts to reduce water activity through super concentration; and (iii) the use of hybrid electrolytes combining the advantages of both aqueous and non-aqueous phases. Then, we discuss different battery chemistries operated with different WIS electrolytes. Finally, we highlight the challenges and future technological perspectives for practical aqueous energy storage systems, including applications in stationary storage/grid, power backup, portable electronics, and automotive sectors.

Almost all the energy we consume is produced from fossil fuels with the subsequent production of CO2 that is the main cause of the ongoing climate crisis. The most promising alternative is a hydrogen-based circular economy where green H2 is produced in renewable electricity-powered water electrolyzers, and electrochemically combined with oxygen to power all our everyday activities in fuel cells. The only commercially available technology in this field are of proton exchange membrane fuel cell (PEMFC) where the ion conducting membrane is based on a perfluorosulfonated polymer (e.g. Nafion® and Aquivion®). The main limit of this technology is related to the relatively low lifetime of the device caused by the degradation of the polymeric chains [1] caused by radical species (•OH •OOH) created, as byproducts of the complicated oxygen reduction reaction, at the cathode. The best strategy to improve the device’s lifetime is the introduction of radical scavenger species in the membrane electrode assembly (MEA). The most promising radical scavengers are cerium oxide nanoparticles embedded either in the polymeric membrane [2], or in the catalyst layer [3]. To improve the compatibility between the inorganic filler and the organic polymeric matrix we synthesized CeO2 NPs decorated with a perfluoroalkyl chain trough a silanization process of the nanoparticles surface (figure1). This is expected to increase the compatibility of the filler with the membrane thus allowing for higher scavenger loads without significant losses in conductivity: the perfluorinated pendant on the oxide NP is expected to anchor it in the hydrophobic domain of the membrane; thus, hopefully, not disrupting the delicate ionic channel network. Furthermore, the decoration is expected to reduce the migration effect that have been highlighted in long-term studies [4] of composite MEAs and improve the mechanical properties of the membrane acting as a physical cross-linker between different polymeric chains. Bot

Hydrogen economy is considered the best alternative to the current fossil fuel-based energy production system; which is arguably the main cause of climate change. It involves the employment of green hydrogen, produced form renewable energies, in fuel cells to sustain today’s massive energy demand. The most prominent technology in this field, are Proton Exchange Membranes Fuel Cells (PEMFCs); which are based chiefly on perfluorosulfonated polymers such as Nafion® and Aquivion®. One of the main factors hindering a wider diffusion of these devices is related to their limited durability, especially in heavy-duty applications where longer lifetimes are required. This is caused by the reaction between various radical species and the ionomer, that result in the disruption of either the backbone or the lateral chains of the polymer. Currently the best strategy to improve the long-term stability of MEAs (Membrane Electrode Assembly) for PEMFC, is to add some fillers that act as a scavenger for radical species; and the most promising one are ceria nanoparticles. They have been added in the ionomer present in the catalyst layer and, more recently, are being dispersed directly in the membranes; both approaches lead to an improvement of the MEA’s lifetime. Either way, however, the nanoparticles tend to migrate, over time, under working conditions; thus, they progressively lose their effectiveness. The decoration of the surface of the NPs with organic pendants, that act as anchoring groups, is amongst the innovative strategies pursued to hinder this phenomenon. Our work is devoted to the synthesis of CeO2 NPs decorated with perfluorinated short chain alkanes ; that anchor them in the hydrophobic domain of the Aquivion® membranes they are dispersed into. This innovative approach is aimed at the improvement of the membrane’s lifetime, without meaningful performances reduction, while also enhancing the mechanical resistance of the ionomer (the decorated nanoparticles act as physical

Highly concentrated aqueous binary solutions of acetate salts are promising systems for different electrochemical applications, for example, energy storage devices. The very high solubility of CH3COOK allows us to obtain water-in-salt electrolyte concentrations, thus reducing ion activity and extending the cathodic stability of an aqueous electrolyte. At the same time, the presence of Li+ or Na+ makes these solutions compatible with intercalation materials for the development of rechargeable alkaline-ion batteries. Although there is a growing interest in these systems, a fundamental understanding of their physicochemical properties is still lacking. Here, we report and discuss the physicochemical and electrochemical properties of a series of solutions based on 20 mol kg-1 CH3COOK with different concentrations of CH3COONa. The most concentrated solution, 20 mol kg-1 CH3COOK + 7 mol kg-1 CH3COONa, gives the best compromise between transport properties and electrochemical stability, displaying a conductivity of 21.2 mS cm-1 at 25 °C and a stability window of up to 3 V in “ideal” conditions, i.e., using a small surface area and highly electrocatalytic electrode in a flooded cell. Careful Raman spectroscopy analyses help to address the interaction network, the phase evolution with temperature, and the crystallization kinetics.

Recent significant progress in performance of anion exchange membrane fuel cells (AEMFCs) is proving this technology to be a meaningful low-cost alternative to commercial proton-conducting fuel cells. This progress has been largely driven by improved water management through electrode layer engineering. The plethora of membrane and ionomer chemistries makes the optimization of the electrode composition often unreproducible, leading to inaccurate performance comparisons. In this study we introduce the distribution of relaxation times (DRT) as an accessible and convenient tool to diagnose the limiting polarization processes in AEMFCs, which significantly simplifies the electrode optimization. To demonstrate the potential of DRT diagnosis, we fabricate cells with different anode electrode compositions simulating the effects of water transport limitations, such as anode flooding and cathode dry-out. The DRT separates and quantifies the contributions to the polarization resistance of the following processes: cathode and anode charge transfer, ion transport in the catalyst layer and gas diffusion. The anode catalyst layer optimization using information from the DRT has helped to increase the peak power density of the current cells from 550 to 690 mW/cm2. We foresee a large potential in using the DRT approach for the diagnosis and optimization of AEMFCs’ operational, structural, and compositional parameters.

Water electrolysis is by far the most appealing method to produce green hydrogen. Among the possible technologies, Anion Exchange Membrane (AEM) water electrolyzers are promising in the medium term, as they make it possible to avoid critical and noble materials as catalyst components. However, AEMs are still lacking in performance and stability, which has become the current research focus. Here, we report the facile and inexpensive chemical modification of polyketone (PK) with a functional unit encompassing morpholinium as the positively charged group, and the fabrication of self-standing membranes. The synthesis products are investigated with an ensemble of physico-chemical and spectroscopic techniques, including solid-state and time-domain NMR, FT-IR, and thermal analysis. The membranes show good Ion Exchange Capacity values in the range 1.48–2.24 mmol g−1. A preliminary electrolysis test shows that the PK-based membrane has performance comparable to that of a commercial one.

Extended interphases are playing an increasingly important role in electrochemical energy storage devices and, in particular, in lithium-ion and lithium metal batteries. With this in mind we initially address the differences between the concepts of interface and interphase. After that, we discuss in detail the mechanisms of solid electrolyte interphase (SEI) formation in Li-ion batteries. Then, we analyze the methods for interphase characterization, with emphasis put on in-situ and operando approaches. Finally, we look at the near future by addressing the issues underlying the lithium metal/electrolyte interface, and the emerging role played by the cathode electrolyte interphase when high voltage materials are employed.

Water-in-salt solutions, i.e. solutions in which the amount of salt by volume or weight is larger than that of the solvent, are attracting increasing attention in electrochemistry due to their distinct features that often include decomposition potentials much higher than those of lower concentration solutions. Despite the high solubility of potassium acetate (KAC) in water at room temperature (up to 25 moles of salt per kg of solvent), the low cost, and the large availability, the use of highly concentrated KAC solutions is still limited to a few examples in energy storage applications and a systematic study of their physical-chemical properties is lacking. To fill this gap, we have investigated the thermal, rheological, electrical, electrochemical, and spectroscopic features of KAC/water solutions in the compositional range between 1 and 25 mol kg-1. We show the presence of a transition between the "salt-in-solvent"and "solvent-in-salt"regimes in the range of 10-15 mol kg-1. Among the explored compositions, the highest concentrations (20 and 25 mol kg-1) exhibit good room temperature conductivity values (55.6 and 31 mS cm-1, respectively) and a large electrochemical potential window (above 2.5 V).

There is a growing demand of electrochemical energy storage, driven by automotive and stationary requirements. Lithium-ion batteries (LIBs) are expected to dominate the market from the current 0.5TWh to about 2.5TWh in 2030. This will lead to great difficulties in the procurement of critical raw materials and in the management of end-of-life systems. From a circular economy perspective, it is necessary to identify reuse and recycling strategies that can make the demand fully sustainable. However, second life and recycling are not mutually excluding, while the final fate of the battery, or at least of its noblest components, should be recycling instead of disposal. In this context, to allow new strategies such as direct recycling of cathode powders, an accurate redesign of the battery system, from the single cell to the modules, which allows ease of separation of the compartments, should be considered. The correct evaluation of the best strategies cannot be separated from an accurate and transparent life cycle assessment (LCA), which would take into account both economic and environmental aspects. Herein, the most advanced recycling methods are analyzed and the issues underlying the efficient reuse and recycling of battery packs from electric vehicles are critically discussed.

Organic-inorganic composites can be conveniently obtained by sol-gel recipes. They can find interesting applications in several fields, including drug delivery, scaffolding, bio-sensing, energetics, etc. Herein, we reconsider and reinvestigate our previous work in the field, by considering the sol-gel synthesis and physicochemical characterization of class-I organic-inorganic hybrids, and by trying to highlight some unifying elements that can be of help for the development of more efficient and precise synthesis methods. Systems based on poly(ethylene glycol) with SiO2 and ZrO2 as the ceramic phase will be discussed. Emphasis will be put on the role played by solid-state NMR spectroscopy in unveiling the interactions at the base of hybrid formation.