A new cathode material, FeS2-decorated carbon nanofiber (CNF), is proposed for Li-S batteries. The structure and physicochemical properties of the material have been engineered to enhance the poor cycling stability typically displayed by sulfur composites. The composite material shows a complex architecture with a matrix of CNF hosting the sulfur and core-shell FeS2 nanoparticles acting as a catalyst for a solid phase conversion-type reaction. This cathode delivers high discharge capacities of 864, 798, 689, 595 and 455 mAhg−1 at C/10, C/5, C/2, 1C and 2C, respectively, with a stable capacity retention of 87% at 2C after 300 cycles. FeS2-decorated CNF has been characterised using several techniques, including in-situ battery measurements at the ALBA synchrotron facility and high-throughput microscopy, giving valuable insights into its charge/discharge reaction mechanism. The excellent performance obtained is combined with the use of just low-cost and abundant elements such as iron, sulfur and carbon, which makes this battery highly promising for the next generation of electrochemical energy storage devices.

Lithium-sulfur (Li-S) batteries are increasingly pursued as an alternative to Li-ion batteries due to their potential for reduced environmental impact. The combination of abundant, low-cost sulfur and its high theoretical capacity positions it as a promising candidate. Typically, Li-S batteries employ a highly porous carbon-sulfur cathode with an organic electrolyte and a lithium metal anode. This setup facilitates the reversible cycling of sulfur to lithium sulfide (S/Li₂S) via intermediate polysulfides, Li₂S_x (where 2 < x < 8). However, several challenges hinder the practical realization of Li-S cells, including poor S/Li₂S mass loadings, rapid capacity fading, low rate capabilities, and the irreversible reactions of polysulfides at the anode. These issues largely stem from an incomplete understanding of the conversion mechanism.

While the formation and dissolution mechanisms of solid Li₂S are subjects of ongoing debate, numerous studies suggest that Li₂S forms via direct electroreduction of Li₂S₂ or longer-chain polysulfides at the carbon-electrolyte interface. The observation that Li₂S deposits are tens to hundreds of nanometers in size and porous indicates a solution-mediated formation process, potentially through the disproportionation of dissolved polysulfides or direct electroreduction of molecular Li₂S₂. Achieving a comprehensive understanding of Li₂S formation mechanisms necessitates a detailed chemical and structural analysis at both atomic and nanometer scales [1], [2].

To extend the practical cycle life of Li-S batteries, integrating sulfur-infused microporous carbon with carbonate-based electrolytes [3] has shown promise. This approach, featuring the formation of a protective cathode-electrolyte interphase (CEI), helps mitigate polysulfide dissolution and reduce capacity fading. However, the mechanism, the factors limiting capacity, rate, and sulfur loadings are not fully understood.

In this context, we present an investigation aimed at deepening the understanding of solid-state sulfur conversion in classical Li-S cell and those with confined spaces. A variety of structure-sensitive and electrochemical techniques have been employed. These include electrochemical impedance spectroscopy (EIS), galvanostatic charge/discharge testing, operando X-ray diffraction, spectroscopy, electron microscopy, and small-angle scattering. Each technique has its limitations, but recent advancements in operando small and wide-angle X-ray scattering (SAXS/WAXS) and small-angle neutron scattering (SANS) have enabled simultaneous structural and chemical insights from atomic to sub-micrometer scales, with time resolutions as short as several seconds.

Two-dimensional (2D) superlattices are rising stars on the horizon of energy storage and conversion[1]. While preserving the distinctive characteristics of their 2D counterparts, they not only significantly enrich the family of 2D materials but also introduce novel functionalities such as adjustable interlayer spacing, entirely new physicochemical properties, and maximized heterojunction effects[2]. However, the intricate and low-yield synthesis procedures impede their large-scale production and application. In this context, we present a simple and high-yield solution-based approach for generating a series of 2D organic–inorganic hybrid superlattices. We demonstrate the substantial potential of these hybrid superlattices and their derivatives in the field of electrochemical energy storage, including applications in metal-sulfur batteries and metal-ion batteries.

Our synthesis primarily revolves around 2D selenide-based hybrid superlattices, exploring dozens of superlattice materials, including WSe2, MoSe2, VSe2-based superlattices. The synthesis route for these materials consistently exhibit remarkably high yields (exceeding 85%), enabling facile laboratory-scale production at the kilogram level. These superlattice materials exhibit physicochemical properties starkly distinct from those of the original selenide-based primitive units. For instance, the PVP-WSe2 superlattice allows for a continuously adjustable interlayer space ranging from 10.4 to 21 Å during annealing (compared to 6.5 Å for the original WSe2 crystal)[3]. This bears crucial significance for ion transport and volume changes during alkali metal ion charge-discharge processes. Simultaneously, the introduction of interlayer components is bound to alter the electronic structure in the bulk phase, causing not only changes in electron transport behavior but also exerting a significant tuning effect on catalytic active centers.

Overall, this work not only establishes a cost-effective strategy for producing new artificial superlattices but also pioneers their application in the field of electrochemical energy storage.

High theoretical energy density and low cost make lithium-sulfur (Li-S) batteries a very promising system for next-generation energy storage. Li-S batteries (LSB) performance largely depends on the reversibility of elemental sulfur to Li2S conversion and the mitigation of the polysulfide shuttle effect. Well-designed sulfur host materials including Fe or Co single atoms embedded on N-doped carbon are proposed to tackle the LSB challenges and enhance its electrochemical performance [1]. The physiochemical characterization of these materials was performed with different accurate techniques such as XRD, XPS, BET, Raman and Mössbauer spectroscopies, HAADF-TEM and TEM. The atomic dispersion of Co and Fe was proved up to relatively large amount. The catalytic effect on the sulfur conversion reactions, using the different structures developed, could be highlighted, by measuring kinetic constants. When comparing these materials with sulfur loadings between 3 and 4 mg cm2 and electrolyte/sulfur (E/S) ratio higher than 8 ml.g-1, the performance in terms of capacity and cyclability are relatively similar. The differentiation of developed materials was only be observed, when the experimental conditions are less favorable, especially in lean electrolyte, ratio E/S equal or lower than 6 mL.g-1. In these conditions, the materials presenting a porous structure including mesopores with a specific surface at least equal to 300 m2 g-1 enable to obtain high performance, with capacity equivalent to those obtained with high E/S ratios. Moreover, the coulombic efficiency is improved by the limitation of the redox shuttle effect.

Lithium-sulfur (Li-S) batteries are a very promising technology to achieve high-energy rechargeable batteries thanks to its high specific capacity (1672 mAh g^-1). Sulfur is an affordable material because of its abundance on the planet and its availability as a waste product of petroleum refinement^[1]. However, the discharge mechanism of a conventional Li-S battery with liquid electrolyte based on the dissolution of lithium polysulfides in the electrolyte leads to numerous issues that impede the performance of the cells: the polysulfide shuttle effect and the corrosion of the lithium negative electrode are two major hurdles faced by Li-S technology. Most importantly, this conventional mechanism requires large volumes of electrolyte to dissolve the active material of the cathode. This results in a high electrolyte to sulfur (E/S) ratio, in which limits the energy density. To achieve a lower E/S ratio, one solution consists in decoupling the electrochemical mechanism from the amount of electrolyte needed.^[2] To do so, some research teams have tuned the electrolyte or the cathode structure to prevent polysulfide dissolution and invoke a so-called “quasi-solid” (QS) reaction mechanism, which limits the dissolution of long polysulfide chains. ^[3] In order to obtain this QS mechanism, one can modify the nature of the electrolyte (e.g. sparingly solvating electrolytes)  or the structure of the cathode (e.g. confinement of the sulfur in carbon nanotubes).^[4]

Initially, we started by fabricating state-of-the-art Li-S coin cells using a standard electrolyte (1.0 M LiTFSI and 0.25 M LiNO₃ in DOL:DME (v:v/1:1)). Although they were unoptimized, our batteries showed promising results (800 mAh cm^-1 after 50 cycles, 2.80 ± 0.16 mg_s cm^-1). These batteries will serve as a foundational benchmark throughout the remainder of the thesis, providing a basis for comparison with future results obtained using QS mechanism batteries. The choice of electrolyte is crucial as it significantly influences the discharge mechanism. Therefore, we also initiated a screening of various electrolytes with limited polysulfide solubility, by measuring their ionic conductivity. Additional experiments will be conducted, such as polysulfide solubility and cycling performance.  

To reduce the environmental impact of our battery cathode, we are planning to use waste rubber from used tires as a starting material.^[5] Tire rubber already contains the main components of a sulfur cathode: sulfur, carbon and a polymeric binder, but in proportions that are not suitable for a battery. One objective of this work will be to increase the sulfur content in the composition of the waste rubber to make it a viable cathode for lithium-sulfur cells. The initial phase of this thesis involved a comprehensive analysis of tire samples (elemental analysis, XRD, FTIR-ATR, ICP-MS). The strategy involves employing inverse vulcanization of sulfur with rubber, aiming to impede sulfur dissolution in the process. Our most advanced results will be shown.

Global demand for power generated from renewable sources, such as wind or solar, is growing. Stationary energy storage is one of the key technologies to ensure stable and reliable power supply despite the intermittent nature of these sources. Stationary storage helps not only to balance short but frequent fluctuations, it can also store large amounts of excess energy for many hours or days and discharge it at time of high demand. High-temperature sodium-sulfur (NAS^®) batteries are well suited for such long-duration stationary storage applications.                                             

NAS^® battery cells consist of sodium as the negative electrode and sulfur as the positive one. A beta-alumina ceramic tube functions as electrolyte, which allows only sodium-ions to pass through. When discharging, sodium is oxidized and sulfur is reduced to form sodium-polysulfide (Na₂S_X). The charging step recovers again metallic sodium and elemental sulfur. This technology is based on abundant, non-toxic materials and provides high energy density with an optimum discharge window of 6 – 8 hours. The NAS^® battery has a design life of 20 years, high capacity retention and an elaborated safety concept.

Since the first NAS^® batteries have been commercialized more than 20 years ago, the total installed capacity is now approaching 5 GWh. NGK Insulators Ltd. and BASF Stationary Energy Storage cooperate to deploy NAS^® batteries worldwide and to develop the next generation of batteries. This presentation will give an overview over NAS^® battery technology and the features it offers for stationary energy storage.

Field effect (Electric, Magnetic) enhancement of catalytic performance refers to improving the efficiency and activity of catalytic reactions through the application of external fields. The field effect can introduce an electric field or magnetic field on the surface of the catalyst to regulate the energy barrier, electron transfer rate and catalytic activity of the catalytic reaction. This method can provide an effective ways to enhance the performance of the catalyst and promote the catalytic reaction. Metal-sulfur batteries(Li, Na) have been widely studied by researchers due to their high theoretical specific capacity (1675 mA h g^-1) and energy density (2600 Wh kg^-1). Due to the "shuttle effect" caused by the solubility of its intermediate product polysulfide, battery failure is caused. In this context, we extend the field effect to the field of metal-sulfur batteries to reduce the polysulfide redox reaction kinetics barrier to achieve high-performance in metal-sulfur batteries.

1. Through external heat-assisted electric polarization, the traditional α-phase PVDF binder without ferroelectric effect is converted into β-phase PVDF with ferroelectric enhancement to anchor polysulfide through electrostatic interaction force while enhancing the lithium ion diffusion resistance. The structure of the PVDF film before and after polarization was analyzed through XRD, Raman and FTIR, and it was found that as polarization increased, PVDF gradually transformed from the α phase to the β phase. The modified electrode can still maintain stable capacity after 1000 cycles at 1 C, and the decay rate of specific capacity is only 0.038%.[1]
2. Apply a constant magnetic field outside the battery and use CoS_x as the catalytic additive.[2] By exploring the impact of the magnetic field generated by the external magnet on the electrochemical performance of the battery, we found that the addition of the magnetic field can significantly improve the adsorption ability of polysulfides and the Li-S reaction kinetics. The CNF/CoS_x/S electrode exhibits excellent electrochemical performance. In the presence of a magnetic field, even at a high current density of 2 C, CNF/CoS_x/S dropped to 315 mA h g^-1 after 8150 cycles, with a decay rate of only 0.0084% per cycle.
3. CoFe₂O₄ catalyst under an external magnetic field assists sodium-sulfur battery to realize high electrochemical performance.[3] This work details the process of growing CoFe₂O₄, VO₂ and Co₃O₄ particles on the surface of CNF using a combination of electrospinning and hydrothermal processes. At the same time, this work systematically explores the process of the prepared cathode material catalyzing sodium polysulfides (SPSs) through ferromagnetic and paramagnetic catalysts under an external magnetic field. DFT calculations show that under a magnetic field, the adsorption energy of SPS on the ferromagnetic catalyst applying a magnetic field increases, and the kinetic barrier for SPS conversion decreases. Experimental results show that the spin-polarized Co ions in CoFe₂O₄ improve the ability to adsorb SPS and the electrocatalytic activity of SPS conversion. Experiments and theory have proven that the magnetic field can polarize the electrons of Co ions, thereby enhancing the adsorption of SPS and its catalytic conversion. The CNF/CoFe₂O₄/S cathode with spin polarization can last for 2700 cycles at 1 C, with a decay rate as low as 0.0039% per cycle. 

In summary, these works not only establish a new catalytic relationship and strategy for the field effect in the redox reaction kinetics of polysulfides, but also provide new ideas for applications in the field of efficient electrochemical energy storage.

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As the demand for high energy density storage increases, lithium-sulfur batteries (LSBs) are being considered as a promising solution. However, before commercialization, they must overcome several limitations, including instability of sulfur cathodes and lithium metal anodes. Considering this, silicon nanowires (SiNWs), with a high theoretical capacity and low discharge potential, represent an interesting alternative anode material capable of meeting this demand. Nonetheless, their synthesis requires a cost reduction to achieve industrial relevance. Our study introduces low-cost catalysts, tin sulfide/or oxide, that allow growing silicon nanowire directly on graphite, producing Si-rich anode composites (over 30%wt of Si). The non-uniform distribution of self-confined conductive silicon nanowires on the surface of graphite takes advantage of their matrix to effectively pad volume changes and significantly reduce the phenomenon of sputtering and capacity fading during lithium insertion and extraction, as well as maintaining the SiNWs' integrity.

Within the ERA-MIN3 project “2BoSS” (2boss.eu), we recently inquired how to improve this process towards a more sustainable material to be included in lithium-sulfur batteries. First we developed a post-synthesis treatment to remove the tin growth catalyst from the composite. Second, we turned to recycled graphite to include this material in a circular strategy in the battery sector.  Third, we used porous carbon obtained from biowaste to synthesize composites with very high silicon content (over 40%wt).

We also optimized a formulation of electrolyte able both to stabilize the SEI of Si-rich anodes and the cycling of sulfur cathodes. Assembly of full cells is under way.

Lithium–sulfur (Li–S) batteries stand out as promising next-generation power systems due to their high energy density, cost-effectiveness, and environmental compatibility [1]. Nevertheless, these batteries are known to suffer from several drawbacks that impede their widespread use in commercial devices, such as the low conductivity of the sulfur cathode, irreversible polysulfide formation and shuttling, and sluggish kinetics [2]. Recently, it has been demonstrated that using binary metallic Prussian Blue Analogues (PBAs) as chemical precursors for obtaining transition-metal chalcogenophosphates (MPSx) is an interesting strategy to address many of the issues that sulfur batteries face. The electronic configuration of the metals in the precursor PBA and final MPSx proves pivotal in enhancing the interaction between the cathode and sulfide species, resulting in improved kinetics and reduced shuttling, accompanied by high sulfur utilization [3]. In the talk, I will delve into the application of the newly discovered high-entropy PBAs (HE-PBAs) [4] as chemical precursors for the preparation of MPSx materials, opening innovative pathways to materials with high electronic disorder. I will underscore the significance of varying degrees of disorder, achievable through meticulous control of the chemical composition of HE-PBAs, in the production of highly stable cathodes (and even anodes) with enhanced electrical performance. Additionally, I will demonstrate how the manipulation of particle properties, such as size, can have a role in shaping the kinetics of the battery.

BATRAW main objective is to develop and demonstrate two innovative pilot systems for sustainable recycling and end of life management of EV batteries, domestic batteries, and battery scraps contributing to the generation of secondary streams of strategically important CRMs and battery RMs. The first pilot will deliver innovative technologies and processes for dismantling of battery packs achieving recovery of 95% of battery pack components and separating waste streams including cells and modules by semi-automated processes for recycling. BATRAW's second pilot will scale and demonstrate efficient pre-treatment and continuous hydrometallurgical recycling of battery cells and modules including innovative steps for C-graphite, Al and Cu separation from black mass and Mn extraction, achieving a recovery of the full range of battery RMs (Co, Ni, Mn, Li, C-graphite, Al and Cu) at selectivity of 90-98%. Innovations wil be scaled and demonstrated in a pilot systems with recycling capacity of 1 ton lithium-ion battery (LIB) packs dismantled per shift (8 hours) and treat 300 kg BM per day. BATRAW outcomes are of strategic importance within the prospects of the exponentially growing EU battery market and reducing EU import dependency of CRMs. The project will further promote the overall sustainability and circularity of battery products and raw materials by developing new procedures for battery repair and reuse, enabling faster diagnostics and conversion of EV packs into second life batteries, delivering eco-design guidelines for battery manufacturing, demonstrating blockchain platform for raw material tracking and supply chain transparency (Battery Passport) and delivering guidelines for safe transports and handling of battery waste. The project aims to maximize market uptake and impact through ambitious C&D&E plan including circular business models, innovations workshops, dissemination in EU platforms, policy briefs and other strategies to reach markets and stakeholders.

Conducting a Life Cycle Assessment (LCA) is crucial for developing Li-S batteries to identify key impact phases and to prevent impact shifting. However, a significant challenge arises from the scarcity of primary data, especially about the use phase and EOL, given the current laboratory-scale status of these technologies. Anticipating improved precision in environmental impact data and the emergence of more reliable and comparable studies with the implementation of the new European Commission regulatory framework, this study presents a prospective LCA on Li-S batteries. The analysis focuses on the technology developed within the 2BOSS project, offering insights into challenges faced and lessons learned.

The consumption of rechargeable batteries has exponentially grown since their first commercialization. Of interest, lithium-ion batteries (LIBs) are currently dominating the market, both for stationary and mobile applications. From one LIB to power a cellphone to a pack of six cells in a laptop or thousands in an electric vehicle (E.V.), the number of LIBs currently in use and in need for end-of-life management in the coming years is tremendous. Furthermore, considering the new regulations following commitments to allow for the energy transition, the E.V. market is expected to continue to grow, which implies a surge both in the international battery demand and their end-of-life management. As a sustainable solution, the secondary use of spent E.V. batteries as stationary application may appear as interesting and profitable. However, such a repurposing of spent E.V. batteries for a less demanding application is a short-term answer, as the end-of-life issue remains unsolved as soon as the second life of this battery reaches its end. In addition, the important increase of demand puts pressure on the stock and on the availability of the valuable elements composing the battery (e.g. Lithium, Cobalt, Nickel and Graphite). These minerals currently extracted from mines have recently been classified as “critical” by Canada. For both these reasons, the LIBs recycling became a necessity as it offers several advantages, including: (i) providing a sustainable feedstock of battery components; (ii) avoiding mining of raw limited minerals; (iii) adding value to a system (i.e. the battery pack) that was meant to be discarded; (iv) avoiding the creation of waste.

The focus here will be placed on the recovery and regeneration of the critical minerals that compose the cathode (28% wt) and the anode (22%wt) of a LIB, accounting for 50% of its total mass. LIBs are primarily powered by layered oxides materials composing the cathode (e.g. Li(Ni,Mn,Co)O₂ and Li(Ni,Co,Al)O₂) and graphite composing the anode. At the end of life, the LIBs are usually crushed to obtain a “black mass” from which minerals must be extracted. Nowadays, most of the spent batteries actually end their life in China, where pyrometallurgy is used (i.e. heating up the batteries to high temperature (e.g. 1000°C)) to recover cobalt, and nickel. However, lithium can not be recovered using the pyro-metallurgical process as it will be lost in the slag, as well as aluminium. Graphite is also destroyed in this process. Another technique is hydrometallurgy to recover the valuable metals in solution as well as the graphite as a solid. Moreover, lithium can also be recovered in this recycling process, by precipitation of lithium carbonate but it generates sodium sulfate Na₂SO₄ as an undesired by-product. The latter is costly to eliminate and as no value on the market. This issue, as well as the large acidic wastewater generated by hydrometallurgy will be tackled during this presentation. On one hand, we will highlight our patented sustainable and economical recycling process developed for the recovery of lithium from spent lithium-ion batteries using a new electrochemical technology. On the other hand, we will explain our developments for the recovery of both valuable metals and graphite through a gentle hydrometallurgy process, all towards pushing forward the concept of circular economy. A perspective regarding post-lithium battery technologies will also be given.