The electrolyte is arguably one of the most critical components of a battery. It controls the available operating voltage through its electrochemical stability window, it supports the flow of the target ion for any given battery chemistry (eg. Li⁺, Na⁺, Zn^2+, Al³⁺ etc….) between electrodes, it limits temperature of operation depending on its phase behaviour and - probably a key function - it can react on the electrodes to form an interphase, known as the solid electrolyte interphase (SEI) whose properties govern the stability and cycle life of the battery.  

Traditional electrolytes currently used for Li-ion and Na-ion devices are not compatible with higher energy-density anodes required for next generation devices, such as Li metal and Na metal anodes. In addition, there is now a recognition that operation at elevated temperatures is desirable for some applications. Therefore, new electrolyte materials are currently actively being investigated for beyond Li-ion technologies. It has recently been shown that, by using an ultra-high concentration of lithium or sodium salt in an ionic liquid (or indeed some organic solvents), it is possible to achieve stable cycling of several high capacity anodes including Li and Na metal anodes as well as silicon and hard carbon anodes.  These electrolytes indicate a decoupling of the alkali metal ion dynamics from the bulk with t_Li+ or t_Na+ transport numbers approaching or even exceeding 0.5. Interestingly, the nature of the ionic liquid cation can have a significant influence on the electrochemical performance, apparently related to the interfacial structuring and the influence on the SEI layer.  In this work we will discuss these non-traditional electrolyte materials in terms of their physicochemical properties, electrochemical behavior and performance in devices.

      Emerging sodium-ion batteries (NIBs) and potassium-ion batteries (KIBs) show promise in complementing lithium-ion battery (LIB) technology and diversifying the battery market. Hard carbon is a potential anode candidate for LIBs, NIBs and KIBs due to its high capacity, sustainability, wide availability, and stable physicochemical properties. Herein, a series of hard carbons are synthesized by hydrothermal carbonization and subsequent pyrolysis at different temperatures to finely tune their structural properties. When tested as anodes, the hard carbons exhibit differing ion storage trends for Li, Na and K, with NIBs achieving the highest reversible capacity. Extensive materials and electrochemical characterizations are carried out to study the correlation of structural features with electrochemical performance, and to explain the specific mechanisms of alkali-ion storage in hard carbons. In addition, the best-performing hard carbon is tested against a sodium cathode Na₃V₂(PO₄)₃ in a Na-ion pouch cell, displaying a high power density of 2172 W kg^-1 at an energy density of 181.5 Wh kg^-1 (based on the total weight of active materials in both anode and cathode). The Na-ion pouch cell also shows stable ultralong-term cycling (9000 hours or 5142 cycles) and demonstrates the promising potential of such materials as sustainable, scalable anodes for beyond Li-batteries.

The demand for versatile and sustainable energy materials is on rise given the importance of developing novel clean technologies to transition to a net zero economy. Here, we present the synthesis, characterization, and application of lignin-derived ordered mesoporous carbons with various pore sizes (from 5 nm to approx. 50 nm) as anodes in sodium-ion batteries. We have varied the pore size using self-synthesized PEOn-b-PHAm block copolymers with different PEO and PHA chain lengths applying the “soft templating” approach to introduce isolated closed spherical pores of 20 nm to 50 nm in diameters. The pore structure was evaluated by transmission electron microscopy (TEM), nitrogen physisorption, and small-angle X-ray scattering (SAXS). We report microstructure analysis of such mesoporous lignin-based carbons using Raman spectroscopy and wide-angle X-ray scattering (WAXS). In comparison with non-templated carbon and carbons templated employing commercial Pluronic® F-127 and PIB50-b-PEO45, which created accessible channels and spherical pores up to approx. 10 nm in diameter, the carbon microstructure analysis revealed that templating with all applied polymers significantly impede the graphitization upon thermal treatment. Furthermore, the gained knowledge of similar carbon microstructures regardless of the type of template allowed the investigation of the influence of different pore morphologies in carbon applied as anode material in sodium-ion batteries supporting the previous theories in the literature that closed pores are beneficial for sodium storage while providing insights into the importance of pore size.  

Magnesium and calcium batteries are considered promising post-Li battery technologies due to the high gravimetric and volumetric densities of metal anodes, their low redox potentials (–2.37 V and –2.87 V vs. SHE, respectively), and natural abundance, which is an important factor in terms of price and sustainability. The main challenge is the development of suitable electrolytes that enable reversible plating/stripping of Mg/Ca with high Coulombic efficiency in a wide potential window, while also being compatible with the metal anode and cathode materials.

In our recent work, we explore the field of advanced electrolytes based on alkoxyborates and alkoxyaluminates. Different salts were synthesized by exchanging hfip ligands for a variety of alcohols with different sterical properties, number of binding groups, and degree of fluorination. A variety of electrolytes for both systems are studied by physicochemical and electrochemical characterization.

The application of new salts along with some additives will be discussed along with the importance of proper electrochemical wiring of cathode composite containing polymerized redox active organic moieties.

1.         Pavčnik, T. et al. Batter. Supercaps (2021)

2.         Pavčnik, T. et al. ACS Appl. Mater. Interfaces (2022)

3.         Lužanin, O., et al. Batter. Supercaps, 6(2), e202200437 (2023)

4.         Lužanin, O., et al. J. Mater. Chem. A, 11, 21553–21560 (2023)

Can aluminum batteries promise enhanced energy density compared to other technologies? The key to high energy density lies not only in the transport of three charges per ion and in the design of a suitable cathode material but also in the (efficient) use of metallic aluminum as the negative electrode.

Currently used electrolytes for aluminum batteries (AlCl3/EMimCl acidic mixtures) can enable plating and stripping but they are extremely corrosive [1]. This drawback opens serious challenges for the choice of components (current collectors, binders, separators, active materials) that are stable in such a corrosive environment. 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. On the one hand, one strategy is to identify corrosive-resistant components, and on the other hand to develop non-corrosive and benign electrolyte compositions [2]. This presentation will give an overview of the current challenges and propose some solutions in terms of materials and combinations to advance the Aluminum battery technology.

Diversification of battery technologies is crucial both to reduce dependence of specific raw materials and, most important, to adapt to specific use requirements including not only performance figures of merit (energy density, power, lifetime etc.,) but also economic and environmental considerations.  Among the different possible rechargeable battery concepts, those based on multivalent charge carrier ions, such as Mg²⁺, Ca²⁺, Zn²⁺ or Al³⁺, have attracted great attention, especially coupled to the use of the corresponding metal as negative electrode. Aside from the case of Zn, which is the most electropositive element that can be plated using aqueous electrolytes, most attention has been placed in Mg based batteries, for which proof-of-concept was achieved already in 2000 while exploration of the analogous systems is much more recent. None of such concepts has yet reached the market, as significant hurdles remain, affecting not only electrolyte and negative electrode (efficiency of plating/stripping process) but also the positive electrode.  [1] In this regard, migration of multivalent charge carrier ions in inorganic hosts has been proved to be sluggish due to strong coulombic interactions which can be diminished by enhancing the covalency of the bonding and moving from oxides to sulfides, which penalizes the operation potential. 

Open framework structures have also recently attracted attention, amongst which Prussian Blue analogues (PBAs) A_xM[M’(CN)₆]_y · zH₂O (A = alkaline metal (mostly K⁺ or Na⁺); M and M’ = transition metals; 0 ≤ x ≤ 2; y ≤ 1) represent an interesting alternative, which has proved excellent performances in Na and K based batteries. [2] Their structure oconsists of a double perovskite framework with (C≡N)⁻ anions bridging MN₆ and M’C₆ octahedra.  A⁺ and H₂O occupy the cubes defined by the transition metal framework. These have shown electrochemical activity in aqueous electrolytes containing multivalent cations but controversies remain as to whether the redox response observed being related to the intercalation of protons rather than divalent ions.

The study of these compounds in non-aqueous electrolytes is appealing, especially if both M and M’ are redox active (e.g. Fe, Mn), and they have shown excellent performance in K⁺ and Na⁺ batteries with very good kinetics and cycle life. The presentation will deal with analogous studies carried out in Mg²⁺ and Ca²⁺ containing electrolytes.  [3] Electrochemical performance, possible side reactions, and operando diffraction studies aimed at unravelling the redox mechanism will be discussed.

The growing interest in room-temperature sodium metal rechargeable batteries (SMBs) for large-scale energy storage applications stems from their potential to serve as a cost-effective alternative to lithium-based batteries. This is attributed to the natural abundance of sodium and its low redox potential (-2.71 vs. SHE).^[1] However, the use of metallic sodium as an anode entails drawbacks such as the generation of a low conductive solid electrolyte interface (SEI), together with dendrites formation during the sodium plating/striping process, which implies short-circuit and safety hazards.^[2] Therefore, the development of advanced electrolytes that enable the use of metallic sodium as an anode is crucial for the overall good performance battery.

On the other hand, the commercialization of SMBs also requires the development of practical cathodes that provide satisfactory rate performance, long cycling life, and high areal capacities. During several years, inorganic active materials such as layered transition metal oxide (LTMO), polyanionic compounds, or Prussian blue analogs (PBA) have been widely studied as cathodes in sodium-based batteries. However, these inorganic compounds present low insertion kinetic, their theoretical capacity is commonly limited to one-electron transfer, and exhibit severe volume alterations during intercalation–deintercalation cycling leading to poor cycling stability. On the contrary, redox-active organic compounds can offer multielectron reactions, present high theoretical capacity, and are able to better accommodate volume changes.^[3,4] However, the low electrical conductivity and the partial dissolution of organic materials in the electrolyte often limit the areal capacity and the long-term cyclability of the battery.

In this communication, it is described the use of a highly concentrated electrolyte (> 7M) based on liquid ammonia, whose formula is NaI·3.3NH₃,^[5] which can effectively stabilize the metallic sodium delivering a coulombic efficiency of 99.8 % during the plating/stripping process, even at very high currents. This electrolyte is utilized in a sodium metal battery (SMB) where the metallic sodium anode is combined with a hybrid anthraquinone-based conjugated microporous polymer as cathode.^[6] Due to the intrinsic textural properties of this compound it is possible to prepare thick electrodes maintaining excellent electrochemical performance.

All in all, the battery depicted here shows an outstanding areal capacity of 7 mAh·cm^-2, never reported before for SMBs. In addition, this battery has demonstrated excellent rate capability up to 250C (37.3 A g^-1, near 70% capacity retention) and stable cycling (80% capacity retention after 4000 cycles with coulombic efficiency close to 100 %). In summary, the combination of a hybrid conjugated porous polymer with an ammoniate-based electrolyte results in a sodium metal battery characterized by high energy and power density, excellent areal capacity and long-term cyclability. This combination proves useful in designing practical Sodium Metal Batteries (SMBs).

The rapidly growing need for energy storage exceeds the energy density of the currently dominant commercial lithium-ion batteries (~200 Wh/kg). Therefore, there is an exhaustive search to find a viable alternative to lithium-ion batteries. Thus, metal-sulfur technology is strongly emerging to become the next-generation of rechargeable batteries. Lithium-sulfur (Li-S) and sodium-sulfur (Na-S) batteries are gaining attention because of their high theoretical gravimetric energy densities, 2615 and 1673 Wh/kg, respectively, as well as the low cost and non-toxicity of sulfur [1][2].

Nevertheless, sulfur has a few drawbacks that negatively affect battery life, being the shuttle effect and its sluggish reaction kinetics the most studied. Among the different solutions proposed to alleviate these problems, it is worth highlighting the trapping of polysulfides through chemical interaction [3]. Recently, it has been demonstrated that the application of a magnetic field to materials with paramagnetic properties can improve cycling performance [4].

One of the materials showing these properties is ZnFe₂O₄ [5]. As a novelty, we propose the use of recycled ZnFe₂O₄ from display wires. Detailed study on the effect of applying a magnetic field on the electrochemical behavior has been carried out. Tests have shown that this sustainable material can act as an efficient sulfur matrix in electrodes with high sulfur content >70% S and high sulfur loading of up to 10 mg/cm². This excellent performance has also been demonstrated for high-rate capability up to 10C. These results overperform those previously published for ZnFe₂O₄ based sulfur cathodes, demonstrating higher specific charge values when applying a permanent magnetic field, especially in long-term tests.

Flexible lithium-ion batteries (LIBs) have garnered significant attention as essential power sources for wearable and flexible electronic devices [1-6]. Despite the increasing interest, achieving optimal flexibility, mechanical stability, and high energy density in flexible LIBs remains a formidable challenge. This study explores the potential of molybdenum carbide (Mo₂C) [7] and vertically-oriented graphene nanowalls (VGNWs) as anode materials for Lithium-Ion batteries.

A bottom-up synthesis approach is employed, involving the deposition of Mo carbide nanostructures on VGNWs using chemical vapor deposition, magnetron sputtering, and thermal annealing processes, followed by in-situ carburization via thermal annealing, resulting in binder-free hybrid electrodes. The resulting Mo₂C/VGNWs hybrids exhibit exceptional structural durability, small particle size, and a porous configuration, promoting enhanced electron and ion accessibility at the electrode-electrolyte interface. SEM results demonstrate varied Mo carbide morphologies based on annealing time, while TEM analyses reveal uniformly anchored Mo₂C nanoparticles on VGNWs.

Electrochemical tests reveal that Mo₂C/VGNWs hybrids outperform VGNWs/Papyex® electrodes in lithium storage behavior. Evaluation of the Mo₂C/VGNW hybrid electrode as a LIB anode material demonstrates superior electrochemical performance compared to VGNWs/Papyex® electrodes. The Mo₂C/VGNW hybrid electrode exhibits a higher first discharge capacity (0.23 mA·h·cm⁻²) compared to VGNWs/Papyex® (0.11 mA·h·cm⁻²) at 1C scan rate. Furthermore, the Mo₂C/VGNW electrode maintains a reversible specific capacity of 0.005 mA·h·cm⁻² after 200 cycles, while the VGNWs/Papyex® electrode shows a significantly lower capacity of 0.001 mAh cm⁻² after the same cycles. The synergistic effects of Mo₂C nanoparticles and highly conductive VGNWs contribute to the superior electrochemical characteristics, positioning the Mo₂C/VGNWs hybrid structure as a promising candidate for high-performance and flexible energy storage devices.

Notably, the Mo₂C/VGNW hybrid electrode demonstrates a progressively increasing coulombic efficiency from 30% to 90.4% in the first 50 cycles, followed by stable performance. The dynamic interactions between Mo₂C nanoparticles and the highly conductive VGNW support contribute to the superior electrochemical performance. This study presents a promising synthesis approach for developing highly efficient and flexible energy storage devices through other carbide/VGNW hybrids.

Lithium–ion batteries (LiBs) are currently leading the portable electronic market due to their great cyclability. However, the current energy demand is pushing the limits of LiBs in terms of energy density (100 – 265 Wh kg⁻¹), cycle life (1000 cycles at > 80% of capacity) and charge/discharge rate capabilities (1C). Aprotic sodium-oxygen batteries (Na-O₂) are promising devices to tackle such energy demands due to their much higher theoretical energy density (1086 Wh kg^-1 based on sodium superoxide discharge product, NaO₂). These conversion batteries reduce oxygen gas to form solid NaO₂, which is deposited on the surface of the cathode during discharge. Rechargeability depends on an efficient charge, where complete redissolution of the superoxide in the organic electrolyte is required to further release all the oxygen back. The size, the distribution, the morphology and the chemical nature of the solid deposits are crucial parameters for the battery performance, due to the electronically insulating nature of NaO₂. Thus, the passivation of the cathode surface by NaO₂ generally leads to a premature death of the battery. Electrolyte formulation has demonstrated to have a profound effect on the morphology of the NaO₂ cubes by affecting their solvation and crystallization processes [1,2]. It is believed that small micrometric particles form a film and promote passivation while large cubes enhance the electron conduction towards the discharge product. However, recent works have demonstrated the importance of the cathode surface chemistry on the nucleation and growth of the discharge products [3-5]. A controlled surface-mediated mechanism enabling the deposition of defined and homogeneously distributed nanometric particles is, in fact, beneficial for battery performance as; i) the discharge product will not insulate the cathode surface by an effective utilization of its surface area and ii) the oxidation of nanosized NaO₂ during charge will be facilitated by nanometric particles at a still conductive electrode.

In this work, edge-defected graphene nanoplatelets will be discussed as cathode in Na-O₂ batteries which act as nucleation points, promoting homogeneous nucleation of nanosized and well-defined NaO₂ cubes at the surface of the conductive graphene air-cathode.

Lithium-ion batteries have delivered a revolution in portable electronics and have begun to unlock electrification of the automotive industry. However, intrinsic performance limitations mean that many applications will be out of reach for lithium-ion technology. We must explore alternatives if we are to have any hope of meeting the long-term needs for energy storage. The Johnson group is focused on tackling the underpinning chemical and materials challenges within next-generation energy devices and in particular batteries.

One such alternative is the Li-air (O₂) battery; its theoretical specific energy exceeds that of Li-ion, but many hurdles hinder its realization. Early cell death, resulting in low capacity and limited rate capability, is one of the most significant problems. Studies of the processes at the positive electrode have shown that this is a result of passivating Li₂O₂ at the electrode surface, poor utilisation of the electrode structure, and degradation of the cell components. Here, we discuss recent advances made in our labs to understand the chemistry within the lithium-air battery and to combat the problems limiting its performance. For example, we have identified a redox mediator able to promote longer discharge and electrode compositions able to facilitate O­­₂ transport throughout the positive electrode. New understanding of the degradation processes have been identified, shedding further light on the failure mechanisms within the cells. Finally the impact of operating in air with the inevitable introduction of H₂O will be considered and we will showcase a demonstrator gas handling system and cell designed to explore these effects.

Energy storage plays, undoubtedly, a fundamental role in the process of total decarbonization of the global economy that is expected to take place in the coming decades. The energy transition to a renewable and sustainable generation is the solution to reduce greenhouse gas emissions and thus achieve the European Commission´s goal of becoming the world´s first decarbonized economy. In this transition, beyond li-ion technologies will play a key role to meet the increasing energy demand that cannot be covered by Li-ion batteries solely. In this scenario, sodium-oxygen have become an attractive alternative due to their high gravimetric energy densities (1605 or 1108 Wh/kg based on Na₂O₂ or NaO₂, respectively) resulting from the use of an oxygen-based phase-change reaction (potentially reducing the weight and freeing up space for other components).

These batteries have been considered as the holy grail of battery research due to their high theoretical energy densities; however, several challenges remain to be solved before commercialization. In this talk, novel approaches on cathode materials and electrolytes will be covered with special focus on sustainability. One of the bottlenecks in this type of device is the kinetic limitations related to oxygen reduction reactions (ORR) and oxygen evolution reactions (OER). Therefore, we have proposed to mimic nucleotides role in cellular respiration by using them as electrocatalysts in metal-air batteries. Regarding electrolytes, we aim to identify an eco-friendly solid membrane electrolyte to achieve stable and high-performing solid-state NaBs by overcoming oxygen crossover from the cathode to the anode. Moreover, the main challenges remaining in this field will be highlighted, along with the future steps required to advance Na-O₂ batteries.

The development of next generation batteries depends heavily on the capability of electrolytes to quickly and selectively transport alkali and alkaline earth metal cations, and form stable electrochemical interfaces. In high energy density metal anode batteries, issues such as dendrite and continuous solid electrolyte interphase (SEI) growth can be addressed by suitable interfacial and electrolyte chemistry.

In the first part of my talk, current understanding of ion transport mechanisms and related electrochemical measurement techniques (impedance spectroscopy, galvanostatic polarization) in soft matter battery electrolytes including liquids, polymers and hybrid (e.g. liquid/oxide and polymer/solid state electrolyte) materials will be discussed. According to this discussion, I will give guidelines and examples of improvements of the relevant electrochemical properties including ionic conductivity and the cationic transference number. 

In the second part of my talk, I will show recent findings related to the electrochemical and chemical growth and transport in SEIs on several alkali and alkaline earth metal anodes in contact with liquid  and solid-state electrolytes. The multitechnique approach involving the measurement of activation energy for ion transport showed that such SEIs are complex composite liquid/solid materials, with sometimes predominant ionic pathways in the liquid phase. The relevance of the native passive layer on alkali and alkaline earth metals, possibility of forming artificial SEIs (e.g. sulfides and Al₂O₃) and electrodeposition through porous SEI will be discussed. Finally, I will show a new modelling approach for treatment of impedance spectroscopy data of symmetric alkaline and alkaline earth metal cells.

      Grid-scale energy storage technologies is important and in urgent need for the Chinese National strategy of “carbon peak and carbon neutrality ”. Among the most energy storage technologies, electrochemical energy storage technologies, such as batteries, shows the great advantages of simple structure and high efficiency, which is developing quickly and widely applicated for varied fields of EES. For the electrochemical energy storage technologies, the electrodes play the key role for the battery performances. Current batteries suffer from low energy/power densities, poor cycling stability and safety issues, it is important to tune the molecule and electronic structure of the electrodes, constructing stable electrode/electrolyte interface, in order to provide more redox active sites, accelerate the ion/electron transfer kinetics as well as guarantee the stable and reversible redox reactions.

      Electrodes with special composition and structure always show attracting electrochemical performances, but are difficult to be synthesized through conventional chemical methods. Multi-physical fields, such as electric, magnetic, plasma, for the precise regulation of the electrodes. Firstly, supercritical condition is introduced for the preparation of heteroatoms doped carbon with ultrahigh doping levels. P doped carbon with an ultra-high doping level (30%) is successfully synthesized and demonstrate an ultrahigh reversible capacity with low potential of 0. 54 V vs Na/Na⁺. Secondly, electronic and thermal fields are coupled for the precisely control of metal valence in the transition metal compounds. Compared to TiO₂, low valence Ti oxides, such as TiO, Ti₂O show higher electronic conductivity and electrochemical reactivity due to metal-like properties. In this work. Ti-O compounds with low Ti valence is prepared through the molten-salts electrosynthesis and deliver a high reversible capacity of 484 mAh g^-1 through the multi-electron conversion reactions. In addition, plasma was introduced for the surface modification of the electrodes for the construction of stable artificial SEI layers with certain species. Artificial SEI layers with certain species of LiF, Li₂C₂ and polythiophene are prepared through the plasma treatment. Benefiting from the high mechanical strength of LiF, low Li⁺ diffusion barrier of Li₂C₂ and flexible structure of the polythiophene, modified Li anodes exhibit an long-term cycling stability of 8000 h with dendrite free structure. When coupling with LiFePO₄, the full cell demonstrate longer cycling performances.

Research and development of lithium-ion batteries (LIBs) has gathered a great deal of momentum in the last two decades due to their potential promising applications in portable electronics and electric vehicles. This is partly due to rapid advancement of inorganic intercalation compounds and carbon-involved composite electrode materials. However, albeit their substantial success, in present commercial LIBs, the urgent need for cost-effective, large-scale, safe, and sustainable battery technologies feeds an ever-growing quest for alternative energy related materials. In this context, substituting traditional metal oxide-based intercalation compounds with organic electrode materials (OEMs) with electroactive organic redox functionalities has attracted the attention of researchers due to the greater abundance of organic compounds, huge synthetic possibilities, lower cost, and safety and sustainability aspects.[1]

Among the different types of OEMs, redox-active polymers (RAPs) are materials of choice due to their high structural diversity, rich and tunable electrochemistry, etc.[2] However, their high electrochemical performance is primarily linked to the use of low polymer mass-loading electrodes (typically below 2 mg cm⁻²) with a high carbon-additives content (20–80 wt%) that together hinders their practicability in real batteries.[3–5] In my oral presentation, I will present an interesting strategy to develop high performance and practical naphthalene-tetracarboxylic dianhydride-derived polyimide (PI) electrodes that are processed into buckypaper electrodes without binder and current collector. This effective electrode fabrication method enables high-mass-loading composite electrodes (up to 55 mg cm⁻²) with low carbon-additive content (20 wt %), which attained high gravimetric (170 mAh g⁻¹), areal (8.5 mAh cm⁻²) and volumetric (205 mAh cm⁻³) capacities with good rate capability (1.6 mAh cm⁻² at 5C; 25 mA cm⁻²) in Li-ion half-cells. To the best of our knowledge, these are most probably the highest values reported for an organic electrode in Li-ion batteries, constituting a great leap forward in the development of practical organic batteries. As a proof of concept, semi-organic full cells were assembled in Li_Graphite||PI, Li_LTO||PI, PI||LFP, and PI||NMC configurations in both coin-type and pouch-type cell prototypes to assess the practicality of these high-mass-loading PI electrodes. Electrochemical performance metrics in terms of capacity, energy and power density (gravimetric, volumetric, and areal) of these full cells were evaluated, along with preliminary cost prediction of practical Li ion batteries for e-mobility application.[6] Both performance metrics (32 mWh cm⁻²) and cost factors (98$ kWh⁻¹) for the presented redox polymer were favourable that could have great prospects for future practical (semi)organic batteries. I believe that this study may be of broad interest to the audience of the conference, providing insights for the development of practical and sustainable energy storage solutions.

Sodium ion batteries (SIBs) are a potential alternative to diversify the energy landscape, beyond Lithium-ion batteries (LIBs), due to their similar storage mechanism and easy technology transfer. Currently, the benchmark anodes for SIBs are hard carbons (HCs), since sodium ions do not intercalate into graphite, the current anode of choice for LIBs. HCs can be produced from a variety of waste precursors that are more sustainable and less geopolitically compromised than natural graphite, mainly concentrated in China.

The electrochemical degradation of SIBs occurs at a higher rate than in LIBs. This can be attributed to the larger electrochemical reactivity of the HC anodes. A deeper operando understanding of the degradation mechanisms in SIBs, coupled with engineering of the materials and electrolyte to ensure that a better and more protective solid electrolyte interface (SEI) is formed, is needed for an accelerated scale up of this technology. In this talk I will show you some of the strategies we have developed for these aims.

The current strong interest in electromotive mobility and the need to transition to an energy grid with sustainable storage devices has led to a renewed interest in sodium ion batteries (SIBs). Amorphous disordered carbons such as hard carbons (HCs) are promising candidates for high-capacity negative electrode materials in SIBs. Their high capacities, however, are often accompanied with high irreversible capacity losses during the initial cycles,[1] while low initial losses are accompanied with moderate capacities.[2] In our research we are aiming morphologically and chemically functional carbons. Morphologically, our target is a local separation of reversible sodium storage and irreversible losses in novel synthetic carbon anodes, using a core-shell concept. On chemical side, we aim at ion-binding functional groups.

We investigated different methods to obtain core-shell structures to restrict SEI formation to the external particle surface, while leveraging the Na storage potential of porous carbon core materials. Moreover, we apply active-site imprinting to realise disting ion-binding features into the core carbons. The electrochemical performance of those materials can be rather easily altered upon removing/exchanging the ions bound to the functional group. Herein, we will focus on the synthesis of zeolitic imidazolate framework (ZIF) based NDCs. Different analytical methods, e.g., physisorption (N₂, Ar, CO₂), XPS, XAS, and NMR, will be used to understand the alteration of morphological and chemical features upon ion exchange.

Two-dimensional (2D) porous frameworks have drawn growing research interest as a new generation of multifunctional materials. Typical 2D porous frameworks include 2D covalent organic frameworks and 2D conjugated metal-organic frameworks, which are characterized by regular porosities, large specific surface areas, and superior chemical stability. In addition, 2D porous frameworks exhibit certain notable properties (e.g., designable topologies and defined redox-active sites), which have motivated increasing efforts to explore 2D porous frameworks for electrochemical energy storage applications.^[1] In this talk, I will show 2D porous frameworks as promising electrode alternatives for next-generation energy storage devices by demonstrating 2D polyarylimide covalent organic frameworks for multivalent metal batteries^[2-3] and 2D conjugated metal-organic frameworks as attractive pseudocapacitive electrodes^[4-5].

[1] Yu et al., J. Am. Chem. Soc. 2020, 142, 12903-12915.

[2] Yu et al., J. Am. Chem. Soc. 2020, 142, 19570-19578.

[3] Yu et al., J. Am. Chem. Soc. 2023, 145, 6247-6256.

[4] Yu et al., J. Am. Chem. Soc. 2021, 143, 10168-10176.

[5] Yu et al., Angew. Chem. Int. Ed. 2023, e202306091.

Aqueous batteries using non-metallic charge carriers, especially of protons, have recently received significant attention.  The proton is the smallest and lightest charge carrier among all cations, which contributes to fast transport kinetics and relatively small structural strain during proton (de)intercalation, leading to promising cycling performance. In recent years, several electrodehost  materials with high-rate capability were explored using acidic electrolytes in terms of the proton’s tiny size and unique hopping transport through the hydrogen bond network. For instance,  defective Prussian blue analog with high-rate performance (4000 C) and excellent cycling stability were observed.  More proton anode materials were explored in metal oxides, mainly including WO3·xH2O, MoO3, H2W2O7, H2Ti3O7, and anatase TiO2.  The α-MoO₃ has attracted much attention for proton storage owing to its easily modified bilayer structure, fast proton insertion kinetics, and high theoretical-specific capacity. However, the fundamental science of the proton insertion mechanism in α-MoO₃ has not been fully understood. Herein, we have uncovered a three-proton intercalation mechanism in α-MoO₃ using a specially designed phosphoric acid surfactant lyotropic liquid crystalline electrolyte. The semiconductor-to-metal transition behavior and the expansion of the lattice interlayers of α-MoO₃ after trapping one mole of protons were verified experimentally and theoretically. Further investigation of the morphology of α-MoO₃ indicated its fracture behavior upon the proton (de)intercalation process, which created ultrafast diffusion channels for hydronium ions. Notably, the first observation of an additional redox behavior at low potential regimes endows a significantly enhanced specific capacity of 362 mAh g^-1.

Nowadays, aqueous rechargeable batteries (ARBs) are emerging as highly promising energy storage alternatives to current Li-ion batteries for stationary applications. This is attributed to their significant advantages in terms of safety and cost-effectiveness, in addition to high performance. Especially, acid-based ARBs stand out as a compelling substitute due to the accelerated proton kinetics resulting from their minimal ionic mass and diminutive radius,^[1] distinguishing them from their neutral^[2] and alkaline^[3][4] counterparts. Moreover, of paramount importance is the proton's ability to achieve exceptionally rapid ionic conduction in aqueous electrolytes, due to its advantageous utilization of the Grotthuss mechanism.^[5]

Conventional acid-based ARBs are based on inorganic electrode materials and face significant drawbacks, including high costs of both anode and cathode material (based on rare elements) and severe active-material corrosion and/or dissolution. Moreover, using a metal anode (e.g., Pb) results in dendrite formation caused by uneven and irregular metal plating on the anode side, in addition to the formation of a thick lead (II) sulphate (PbSO₄) passivation layer.^[2] As a consequence, battery cycle stability is seriously impeded, possibly with short-circuit risks and safety compromises.

Recently, organic electrode materials (OEMs) are re-emerging as green and sustainable alternatives over traditional inorganic materials as they offer distinct advantages. First, they are composed of readily available and cost-effective elements (C, O, N, H). Moreover, by their distinctive ion-coordination mechanism, they can interact with different charge carriers (Li⁺, Na⁺, H⁺, Zn²⁺, etc), finding application in different battery technologies.^[2] Furthermore, under acidic conditions these materials are less prone to the dendrites formation, corrosion, and/or dissolution, common issues faced by their inorganic counterparts.

Recently, we demonstrated the rapid kinetics, good electrochemical performance and excellent robustness of a new conjugated microporous polymer based on phenazine (named IEP-27-SR) in 1 M H₂SO₄ electrolyte.^[6] Here, I will present our recent results on the use of this anode (IEP-27-SR) in combination with an electrodeposited MnO₂-based cathode in a full acid battery. The full battery not only reached an impressive number of cycles (20000 at 30 C with 83% retention) but also could withstand high current densities (100 C, yet achieving 40 mAh g^-1) using 2 mg cm^-2 polymer mass loading anode. Moreover, in this study we could increase the polymer mass loading up to 30 mg cm^-2, while keeping its content high (80 wt%) in the electrode. This enhancement contributed to a significant increase in the areal capacity of the aqueous battery up to 2.8 mAh cm^–2, while maintaining a noteworthy value of 1 mAh cm^{- 2} even under the extreme high current of 79.6 mA cm^-2. This porous polymer//MnO₂ battery offers a sustainable and cost-effective alternative to the conventional acidic battery (e.g., PbO₂ / / Pb), without compromising its performance, paving the way toward practical and sustainable energy storage solutions.

Large-scale energy storage is a key technology for efficient integration of renewable energy generation into the grid and the development of smart grids. Among various energy storage technologies, electrochemical energy storage stands out as a flexible and efficient option, making it an important direction for the development of utility-scale power storage. Liquid metal batteries based on liquid metal electrodes and molten salts electrolytes, with the merits of long-lifespan, low-cost, and high-safety, shows … in large-scale energy storage applications. This article focuses on the key materials and technologies of liquid metal batteries, demonstrating our team's recent research progress at three aspects: materials, devices and energy systems. A novel strategy of alloying liquid electrode for liquid metal batteries was proposed, and a series of high-performance electrode material systems were developed that achieve a high battery energy density of 156 Wh/kg. Moreover, a multi-physics coupling model of liquid metal battery was constructed and revealing the mechanisms and migration laws governing mass transfer at liquid-liquid interfaces. Furthermore, we have put forward a strategy for stabilizing large-scale liquid-liquid interfaces through internal field restriction combined with external active regulation, which enabled the cycle life of Li-Sb-Sn liquid metal battery exceeded 15000 cycles. Based on those strategies, 600 Ah high-capacity liquid metal batteries were constructed. Moreover, we have proposed control strategies for electro-thermal coupled energy storage systems and built a 5 kW liquid metal battery energy storage system.

Critical materials are those which have a supply chain risk and are of high economic importance, this means that criticality is unique to each area of the globe, due to the sourcing of these different materials. In Europe, the critical materials list published in 2023 shows lithium, graphite, phosphate and phosphorous, silicon, cobalt and manganese, all classified as critical. Nickel is although, a strategic material, and with carcinogenic implications is not currently classified as critical. This assessment is dynamic due to changes in the sourcing, supply and also recycling levels of these important elements and materials. With the new battery passport and EU battery directive regulations, 50% of lithium recovery by 2027 and 80% by 2031 from spent lithium-ion batteries. SLI and EV batteries will require a recycled content of 16% for Co, 6% Li and 6% Ni, and recycling efficiency is 50% by 2025. Environmental and social impact needs to be understood throughout the life cycle of the battery, with supply chain due diligence. By 1^st of Feb 2028, a full impact assessment of battery life cycle, or LCA must be supplied, including the recycled content sources.

In this work we look at optimisation of lithium-ion and sodium-ion technologies and the investigation of cathodes and anodes at low and elevated temperatures. In particular a co-doped lithium nickelate is discussed, and its performance in a full cell. By co-doping the layered nickelate with boron and tin, the cathode material has improved low temperature performance properties. In addition, the performance of hard carbon in a sodium-ion system is also discussed, and its performance at low and elevated temperatures.

The transition to “green energy” relies heavily on energy storage devices, especially lithium-ion batteries (LIBs). Even though new battery chemistries are emerging and pose advantages, waste associated with all batteries requires adequate treatment. Just in this decade, about 11 million metric tonnes of spent LIBs will be disposed, being a source of refined, critical materials such as Li, Co and Ni.¹ Hydro- and solvometallurgy are recycling strategies that are showing industrial potential for a more efficient and greener process.² However, the latter is often dictated by the amount of corrosive reagents, waste streams and downstream processing required. Hydroxylated solvents such as glycerol or gallol- and cathecol-based polyphenols can coordinate with metals. Thus, their application, individually or as components of other systems can occur.

In this work, the versatility of these solvents for metal recovery from spent LIBs is expanded, by using them in both liquid and solid state.

As liquids, these solvents were combined with low HCl concentrations and high water content to achieve leaching of Co, Ni and Mn from NMC materials. The increased chloride activity, a promoting ligand for metal dissolution, and direct coordination by the hydroxylated solvents were relevant factors for metal dissolution.

As solids, when combined with [2-(methacryloyloxy) ethyl] trimethylammonium chloride, these solvents could be photopolymerized into absorbing polymers. These could be used in a simple and cyclic process to extract metal ions such as Co, Ni and Li from solutions containing a complex mixture of metals present in spent batteries. Results showed that the hydroxylated solvent, especially glycerol, contributed to maintain the mechanical and structural integrity of the polymers, as well as improving the overall metal absorption capacity of the material.