Secondary raw materials, derived from battery recycling, is considered a valuable source of critical materials by Europe. State-of-the-art recycling processes based on pyrometallurgy and hydrometallurgy recover critical elements such as lithium, nickel or cobalt either as metal alloys or metal salts, which can then be transformed by new synthesis into cathode active materials (CAM). Direct recycling provides an interesting alternative, which retains the active material structure, and thus avoids the step of CAM synthesis.

In the short-term, direct recycling is particularly attractive for production scrap, where the degradation of the CAM is minimal. In comparison, direct recycling of end-of-life materials is more complicated, as structural defects must be repaired and lost lithium must be replaced. The situation is then more complicated when the recycled materials are based on cathode chemistry that are no longer considered state-of-the-art. This contribution will discuss the reuse of active materials recovered from direct recycling processes, including a discussion of upcycling old CAM stoichiometries.

In the development of more sustainable rechargeable batteries, battery safety, and in particular flammability, has become of greater interest. Non-flammable or flame-retarding liquid electrolytes are currently under development.[1] They are designed to offer the benefits of a conventional electrolyte, e.g. high ionic conductivity and wettability, but with the additional safety aspects. A common challenge, however, is the detrimental reaction of such electrolytes at the electrode-electrolyte interface (e.g. solvent co-intercalation leading to graphite exfoliation, or the formation of resistive solid electrolyte interphase (SEI) layers), resulting in poor performance.

Recent studies have shown several fluorinated carbonates as well as organophosphates as being promising candidates as non-flammable solvents or flame-retarding co-solvents/additives. One example of those we have investigated is bis(2,2,2-trifluoroethyl) carbonate (TFEC), which was used as a co-solvent with state-of-the-art carbonate ester solvents.[2] Comparable electrochemical performance was achieved when assessed against a benchmark, while very high TFEC fractions led to increased interfacial resistance and poor performance.

Electrolytes based on a non-flammable solvent, 1,1,1-trifluoroethyl methyl carbonate (FEMC), have also shown promise for their non-flammability attributes and other properties, but require approaches to stabilise the interfaces. Two such strategies are presented; the use of electrolyte additives, and interface engineering by pre-passivation.[3,4] The interfacial behaviour of FEMC-based electrolytes will also be discussed including properties of the formed SEI.

The escalating global demand for energy storage systems has intensified research into sodium-ion batteries (SIBs) as a sustainable alternative to lithium-ion batteries (LIBs), driven by geographical dependency and supply chain risks of lithium metal and other elements involved in LIBs. [1]
Hard carbon stands out as the most promising SIB anode material due to its disordered microstructure, characterized by curved graphene sheets and randomly distributed porosities that provide abundant sodium storage sites through adsorption, intercalation, and nanopore-filling mechanisms. [2]
Recent advances highlight bio-waste precursors, such as pine pollen, lotus root, or Wood fiber, and so on, as sustainable feedstock for hard carbon synthesis, aligning with circular economy principles and EU Battery Regulation 2023/1542 sustainability mandates with its carbon footprint. [3-4]
This study systematically investigates the influence of the pre-treatment washing media on the structural and electrochemical properties of sugar beet pulp-derived hard carbon anode materials, as a sustainable feedstock for hard carbon synthesis, which is a regionally abundant agricultural byproduct in Germany. [5-6]
Precursor optimization with pre-treatment process followed by pyrolysis at 1100°C under argon, which enhanced turbostratic domain alignment, as Raman spectroscopy indicated, and closed-pore formation, confirmed by BET and SAXS analysis, leads to enhanced electrochemical performance of hard carbon anode materials. These findings offer valuable insights into the design of sustainable, high-performance anode materials for next-generation sodium-ion batteries. 

The need for battery technologies with higher energy densities and improved sustainability has motivated a large body of research into new potential electrode materials for rechargeable lithium- and sodium-ion batteries.  However, in many cases, characterising the lithium/sodium-ion (de)insertion mechanisms of these new materials presents significant challenges to conventional crystallographic analysis, as disordered or nano-sized phases may form, some of which may be metastable and exist only within the battery. Here, I will present our recent work detailing how pair distribution function (PDF) analysis - a total scattering technique which is sensitive to both local and long-range structure – has been applied in situ to give highly consistent data sets from which subtle changes to local structure during electrochemical cycling can be resolved. PDF data is analysed alongside complementary methods such as x-ray diffraction, solid-state NMR, x-ray absorption spectroscopy and theoretical calculations to gain insight into a range of potential new electrode materials, including disordered rock salt lithium-cathodes and hard carbon sodium-ion anodes. I will discuss the how these structural insights may aid future electrode material discovery and design.

Key words: lithium-ion batteries, sodium-ion batteries, sustainability, in situ studies, pair distribution function analysis, structure-property relationships.

Boosted after their commercialization in 2023, Sodium-ion batteries (SIBs) are well positioned to become the energy storage system of choice for stationary applications and complementary to Li-ion in electromobility. This is a sustainable and low-cost technology that does not rely on critical raw materials and guarantees widespread availability free of geopolitical constraints, hence avoiding most of the drawbacks of lithium-based technology. However, SIBs energy density has not yet reached the performance levels of LiFePO₄-based lithium-ion batteries (LIBs), partially hindering their application in other sectors. One of the most promising cathode materials, namely the P2-type layered oxides, is affected by irreversible sodium consumption during solid electrolyte interphase (SEI) formation and low sodiation degree: about 2/3. These two factors are the main drawbacks behind SIB’s underperformance. Solutions to these problems have been attempted with limited success and significantly hindering the fabrication cost of Na-based cells. We had a look at quick and low-cost metallization processes used in low value products, such as candy wrapping, to develop a scalable and cost-effective sodiation process based on Na thermal evaporation. This method solves the incomplete sodiation degree of P2-type sodium layered oxides, thus overcoming the first irreversible capacity as demonstrated by manufacturing and testing all solid-state Na doped-Na_~1Mn_0.8Fe_0.1Ti_0.1O₂ǀǀPEO-based polymer electrolyteǀǀNa full cells. This polymer has proven to be suitable for other cell configurations with sodium-deficient electroactive materials that will be presented here. The proposed sodium physical vapor deposition method opens the door for an easily scalable and cost-efficient strategy to incorporate any metal deficiency in the battery materials, pushing further the battery development.

The global move towards net zero economies requires suitable energy storage solutions. Lithium-ion batteries (LIBs) lead the way in battery technology, but their increasing demand causes problems due to the low abundance and high cost of lithium and precious metals commonly used in the cathode material. Sodium-ion batteries (SIBs) are an attractive alternative that have significant sustainability advantages over LIBs. Unlike lithium, sodium is widely abundant and evenly distributed across the globe. The sustainability of SIBs is further improved as they allow cobalt-free cathodes to be used and the copper current collectors at the anode (used in LIBs) to be replaced by aluminium.^[1]

This presentation focuses on the electrolyte for sodium-ion batteries, where the benchmark salt is NaPF₆, which is appropriated from LIBs. While NaPF₆-based electrolytes give high ionic conductivity and stable long-term battery cycling, NaPF₆ is hygroscopic and decomposes to give toxic HF and POF₃ etc.^[2] This presentation discuses the properties of NaPF₆ electrolytes in carbonate solvents and the effect on electrolyte concentration, where lower concentrations give comparable cycling performance in sodium-ion coin cells. This allows for reduced battery manufacturing costs and improved safety, reducing the amount of HF.^[3]

Using alternative electrolyte salts to NaPF₆ are then discussed, with the aim of moving to a safer battery electrolyte. Sodium bis(trifluoromethylsulfonyl)imide (NaTFSI) is an emerging alternative electrolyte salt that is nontoxic and has high thermal stability. However, there are concerns about aluminium corrosion of the current collector.^[4] This presentation discusses aluminium corrosion when using NaTFSI in carbonate solvents and compares the performance of NaPF₆ and NaTFSI electrolytes in SIBs. Lastly, this presentation will discuss the challenges of non-fluorinated electrolyte salts and potential anions that can be used.^[5]

The ecological transition has spurred the development of energy storage, and today Lithium-ion batteries (LIBs) dominate advanced electronics and EVs due to high energy density and long life. However, lithium's scarcity and price volatility hinder meeting growing demand. Sodium-ion batteries (SIBs) are emerging as a promising alternative, especially for large-scale storage and hybrid vehicles, owing to sodium's abundance and low cost. SIBs currently have lower energy density than LIBs due to sodium's atomic properties and standard potential. Efforts are focused on improving SIB performance, particularly electrode materials. Finding suitable negative electrode materials for SIBs with high capacity, stability, and appropriate voltage is a major challenge, as graphite, ideal for LIBs, doesn't work well with sodium ions in conventional electrolytes. Hard carbon has gained attention as a promising SIB intercalation material with notable charge storage capacity, influenced by its structure and surface properties.[1] HC presents, however, a limited volumetric capacity.  

On the other hand, alloys-type materials, forming stable alloys with sodium, have been heavily studied. [2-4] They often involve multiple electron exchange, leading to high gravimetric and volumetric specific capacities (with 670 mAh/cm³ for Sb) for high-energy SIBs. Sb exhibits a complex but highly reversible electrochemical alloying reaction with Na, resulting in good cyclability despite very large volume expansion, which can actually be partially absorbed by a suitable electrode formulation.[5] This volume expansion during cycling causes nevertheless unstable SEI formation, electrolyte consumption, and poor coulombic efficiency.

SIBs technology is maturing, with companies like Faradion, Novasis, HiNa, and Tiamat emerging, mostly using hard carbon anodes. Tiamat, a French pioneer, uses polyanionic cathodes Na₃V₂(PO₄)₂F₃ (100-120 Wh/kg) in its first generation and lamellar oxides (140 Wh/kg, aiming for 180 Wh/kg) in its second. While positive electrode progress is significant, negative electrodes still rely on hard carbon with limited capacity. A recent study demonstrated promising performance for Sb-based negative electrodes in SIBs.[6]

To boost the volumetric capacities of its negative electrodes, Tiamat company decided to launch a study on Sb-carbon composites. The presented study focuses on antimony (Sb) alloy based negative electrodes, aiming to improve gravimetric and volumetric capacity, playing with electrode formulations parameters. Carbon/Sb composites were prepared either by Sb incorporation in hard carbon or by mechano-synthesis of Sb/carbon. Full cells of the as-prepared composites were tested against Tiamat's cathode (NVPF) in full SIBs.

Thanks to many optimizations of Sb (with theoretical capacity of 660 mAh/g) based electrode formulation, higher gravimetric and volumetric capacities than HC were obtained. These latter depend strongly on the electrode preparation (carbon/Sb ratio and mixtures, conductive additives, electrolytes…). In conclusion, the use of antimony in the composition of negative electrodes material in SIBs offers significant advantages in terms of gravimetric and especially volumetric capacity.

In recent years, sustainable battery systems based on Na, Ca, Al, Cl, and Mg have been studied as a complement to Li-ion batteries. Theoretically, the use of aluminum as the negative electrode would bring some important advantages, such as high theoretical specific gravimetric and volumetric capacities, comparable to those of lithium-based systems. However, this emerging technology presents challenges due to the high corrosivity of the commonly used non-aqueous electrolyte AlCl₃/(EMIm)Cl [1-2].

The latest research on cathodes for aluminum batteries includes carbon-, metal oxides-, and metal chalcogenide-based materials. Carbon-based materials have shown excellent cycling stability and their mechanism is based on the insertion and disinsertion of chloroaluminate anions ([AlCl₄]^- and [Al₂Cl₇]^-). Metal chalcogenides have been studied widely. Specifically, in cobalt selenide, it is believed that the high polarizable Al-Se/S bond allows the insertion/extraction of Al³⁺ and takes advantage of the three-electron redox reaction. [2-3]

In this work, we have examined cobalt selenide via in-situ and -operando XRD to determine the interactions happening at the material during the first cycle, combined with a series of electrochemical and ex-situ characterizations and this way unveil the energy storage and degradation mechanism of CoSe. The results indicate that during the first cycle, CoSe undergoes a phase transition to CoSe₂, accompanied by structural disorder and a loss of long-range crystallinity. This transformation impacts cycling stability causing cobalt dissolution and migration to the aluminum anode.  Understanding the cathode processes during cycling could guide the development of high-energy-density, high-power, and stable electrodes for aluminum batteries.

Multivalent battery technologies may alleviate some inherent problems connected with resources and value chains of energy storage solutions. If based on metal anodes they may also improve performance – this is especially the case for calcium batteries that also have the promise of high cell voltages. However, the layers that form at calcium metal anodes in contact with electrolytes are problematic as they in general are very stable and do not allow for any fast ion transport. In addition, the divalent Ca²⁺ keeps a very stable first solvation shell, making de-solvation at the very electrolyte/electrode interface problematic. Here we highlight a number of different routes to possibly overcome these problems by careful design of the electrolyte, including concepts beyond liquid electrolytes and use of organic cathodes [1-5].

References:

1. “Local structure and entropic stabilization of Ca-based molten salt electrolytes”, J. Timhagen, C. Cruz, J. Weidow and P. Johansson, Batteries & Supercaps, 2024, e202400297.
2. “Local structure and dynamics in solvent-free molten salt Ca²⁺-electrolytes”, C. Cruz-Cardona and P. Johansson, ChemPhysChem, 2025, e202500090.
3. “Effects of fluorinated additives in molten salt electrolytes for calcium batteries”, C. Cruz-Cardona and P. Johansson, Batteries & Supercaps, 2025, e202500239.
4. “Solvent-Mediated Electrolyte Design for Calcium Metal Batteries”, Z. Slim, C. Cruz-Cardona, C. Pechberty, T, Hosaka, Z. Mandić, V. Panic, and P. Johansson, submitted.
5. “Electrochemistry of Calcium Metal Electrodes in Three Different Electrolytes”, G. Mihalinec, A. Bafti, K. Kvastek, P. Johansson and Z. Mandić, submitted.

The energy density of state-of-the-art lithium-ion batteries is approaching its theoretical limits, prompting the search for alternative energy storage systems. Multivalent batteries based on magnesium and calcium offer a compelling pathway forward due to the high volumetric and gravimetric capacities of Mg and Ca metal anodes, their low redox potentials (–2.37 V and –2.87 V vs. SHE, respectively), and their natural abundance. A major bottleneck for both technologies is the development of electrolytes that support efficient, reversible metal plating/stripping while remaining electrochemically stable and compatible with cathode hosts.

Our recent work has focused on the development of Mg and Ca electrolytes based on fluorinated alkoxyborate and alkoxyaluminate salts. We investigated different synthesis approaches, variation of the fluorinated alkoxy ligand (using alternatives to the widely employed hexafluoroisopropoxy - hfip), as well as the substitution of the central atom (boron vs. aluminum). The electrolytes were systematically characterized in terms of their physicochemical properties, electrochemical performance, and oxidative stability.

In the case of Ca, where a relatively low redox potential and high reactivity of the metal surface increase the risk of electrode passivation, we further investigated the effects of solvent purity and other factors influencing the reversibility of Ca plating/stripping, including substrate selection and its impact on nucleation and deposition behavior.

Our work provides an overview of the design principles, performance metrics, and practical considerations for advancing alkoxyborate/aluminate-based electrolytes, highlighting their potential for use in next-generation multivalent battery technologies.

Concerns related to future supply of critical materials for Li-ion Batteries (such as Li, Co and Ni) urge to intensify the discovery of alternative battery chemistries, which rely on more abundant materials. Among several options, rechargeable aluminum (Al) batteries (RABs) are promising sustainable electrochemical energy storage systems due to their claimed high safety standards, low cost, and lightweight materials. However, their application is limited by the corrosivity of the chloroaluminate IL-based electrolyte, which is currently the only type of electrolyte able to plate and strip Al efficiently.

This drawback opens several challenges for the choice of electrodes and cells components such as current collector, binder, separator, active materials etc. that should be compatible with the electrolyte [1]. This crucial issue urges to be overcome to advance Al batteries from simple scientific curiosity to real competitors in the realm of energy storage systems.

In this context, this presentation will give an overview of the current challenges and propose some solutions in terms of materials and combinations to advance the Rechargeable Aluminum Battery Technology.