Rechargeable aqueous Zinc (Zn) batteries are one of the emerging beyond lithium-ion batteries that could fulfil the requirements of cost-effective, safe, and reliable large-scale storage systems.^[1,2] Zn metal is abundant, globally available, non-toxic and stable under air and humid atmosphere, with a promising theoretical capacity of 820 mA h/g.^[3] However, aqueous Zn batteries encounter several degradations upon cycling due to the dendrite formation, poor Coulombic efficiency and hydrogen evolution reaction in dilute electrolytes.^[4]

In this work, we report eutectic aqueous electrolytes based on Zn and lithium /or sodium salts at different ratios with very low water content. The cost-effective and fluorine-free electrolyte shows a high electrochemical stability window (~3V), which enables reversible and uniform Zn electrodeposition during long-term cycling. The eutectic aqueous electrolytes also demonstrate a low glass transition temperature allowing a wide temperature-range battery operation. This work significantly provides an effective strategy for high voltage and low-temperature aqueous Zn metal batteries.

Despite its resounding success, lithium ion battery technology has some drawbacks that has motivated researchers around the world to look for future alternative battery technologies. These include safety issues, material abundance and cost, and geographical distribution of lithium.  Aqueous zinc ion batteries are currently one of the most actively investigated battery technologies in the hope that it can one day replace lithium ion batteries. This is because aqueous zinc ion batteries are safe, environmentally friendly, use more abundant and cheaper materials, have somewhat suitable redox potential, which can minimize side reactions in aqueous electrolyte, and divalent charge which increases energy density.  Despite these promises, aqueous zinc batteries suffer from several side reactions that degrade their stability and Coulombic efficiency. We have been developing strategies to mitigate these effects, including cathode material design, anode material surface treatments and passivation, and electrolyte and solvation structure engineering. In this talk, I will discuss some of the recent results from our group aiming to address these issues in zinc metal batteries.

HN Alshareef et al,  Advanced Materials  2022, 34, 2106937

HN Alshareef et al, J. Am. Chem. Soc. 2022, 144, 16, 7160–7170

HN Alshareef et al, Energy Environ. Sci., 2021, 14, 4463–4473

HN Alshareef et al, ACS Energy Letters 2022, 7, 1, 197–203

Currently, the only metal-air technology developed at high TRL is represented by the zinc-air primary battery (ZAB)^[1], for a small number of applications, such as portable hearing aids, railway signalling, electric fence, and generally low-power/low-consumption long term uses. Although presenting many green advantages, like the intrinsic safety and non-toxicity of the aqueous electrolyte, use of abundant and recyclable Zn, absence of expensive or precious metals, ZABs’ barrier to larger and stationary applications (to compete with the already mature Li-ion, Ni-Zn, or lead-acid technologies)^[2] is mainly represented by electrical rechargeability (i.e., developing a bifunctional cathode) and durability of the liquid electrolyte (i.e., leakage and/or evaporation of the KOH-based liquid solution)^[3].

In this work, we survey the actual developments in electrically rechargeable ZAB (ERZAB) and analyse the selection criteria of materials by general and specific constrains, suggesting emerging directions for industrial development, guided by a sustainable point of view. ZABs should switch from conventional liquid electrolytes to gelled electrolytes, based on naturally occurring biopolymers; for the cathode, engineered mixes of specialized catalysts for oxygen reduction and evolution reactions (ORR/OER), not based on critical raw materials (CRMs), should be investigated, pursuing tuneable wettability and long-lasting durability of the cathode. There is an extensive literature about bifunctional cathodes for ERZABs^[4,5], but performance validation should go more towards longer cycles and higher depth-of-discharge (DoD). Finally, interesting electrolyte and cathode materials are tested, and preliminary results are discussed to establish the next steps for future research and developments.

In this presentation, we report the impact of electrolyte solvents (EC:DEC and diglyme) with NaPF6 on the cycling stability and rate capability of Na2Ti3O7 (NTO).  This material has been widely investigated as an anode for SIBs because of its reasonably high specific capacity (177 mAh g-1) and low insertion potential (0.2 V vs. Na+/Na, outside the stability window of electrolytes). However, its rapid capacity decay and rate capability have been highly linked to the formation of an unstable and thick SEI layer. Yet, many studies have focused on the improvement of NTO properties and to date no alternative electrolytes have been proposed. Overall, we observed that the electrochemical performance of Na/NTO half-cells in DiG outperformed that in the EC:DEC solvent in terms of specific capacity, rate capability and cycling stability. Furthermore, we provide a detailed interfacial analysis of both the SEI layer and charge-transfer processes using PES, electrochemical impedance spectroscopy and operando electrochemical AFM under different cycling regimes to explain the enhanced electrochemical behaviour observed in DiG, which results from the formation of a stable, thin and compact SEI.

Rechargeable lithium-ion batteries (LIBs) have been recognized as the most successful energy storage devices with an energy density increase of about 7-8 Wh kg^-1 per year, now reaching between 260 and 270 Wh kg^-1. However, the massive growing market of portable electronic devices, electric vehicles, stationary grid storage, etc. and the safety problems resulting from this technology involve demand for alternatives. Among the intensely studied technologies (i.e., Na-ion batteries, K-ion batteries, Li-sulphur batteries, solid state batteries, Li/Na-air batteries, etc.), Na-ion batteries (NIBs) represent a promising alternative to Li-ion batteries because sodium is widely available and exhibits similar chemistry to that of LIBs.

However, a major challenge of this technology lies in the development of anode materials because graphite, the reference anode used in Li-ion batteries, intercalates only small amounts of Na ions. Hard carbon (HC) has been found to be more suitable anode candidates, being able to reach specific capacities of around 300 mAh g^-1. This is possible due to its disordered complex structure combining graphitic domains and micropores, being recognized as a non-graphitizable carbon. Moreover, they can be synthesized from a large number of bio-sourced precursors (i.e., cellulose, carbohydrates, bio-wastes, plants, etc.), offering thus the possibility to develop eco-friendly anodes.

In this context, our team proposed to develop hard carbons from a series of bio-sourced precursors: natural polyphenols¹ and biopolymers. More precisely, five natural tannin based-polyphenols and five biopolymers were selected to synthesize hard carbons, following a single pyrolysis process at 1500°C, under Ar. Their carbon content, morphology, structure and texture were studied by several techniques. These complementary analyzes confirmed the formation of typical hard carbon structure but also the presence of some residual inorganic compounds, inherently induced by the parent precursor.

HCs electrochemical performance were evaluated versus Na metal, in coin cells. Reversible capacities of around 300 mAh g^-1 were obtained for most of the materials with an initial Coulombic efficiency between 81% and 88%.

Finally, the electrochemical performance was plotted versus different physico-chemical properties of the hard carbon materials and several strong correlations could be found.

This simple approach provides new possibilities for the use of bio-sourced precursors as electrode materials for NIBs, as they provide a reliable, natural, renewable, nontoxic, and low-cost resource for hard carbon production.

The omnipresent Li-ion batteries are reaching their energy density limitations. At the same time, energy storage demands are drastically increasing, motivating researchers to pursue new battery systems. Due to the bivalent nature of ions, low redox potentials, high gravimetric capacities, and natural abundance, Mg and Ca metal anode batteries are considered as promising post-Li energy storage systems. One of the main challenges of both systems is the development of electrolytes.

Fluorinated alkoxyborate-based electrolytes were introduced into Mg and Ca batteries a few years ago and presented significant progress over the previous generations of electrolytes in terms of overpotentials, stability, and Cl-free character.¹ Specifically, Mg[B(hfip)₄]₂ and Ca[B(hfip)₄]₂ (hfip = 1,1,1,3,3,3–hexafluoroisopropoxy) served as model compounds to show that weakly coordinated anion with a high degree of fluorination enables large charge delocalization, decreases the anion–cation interaction, and consequently reduces the ion-pair formation.² Additional improvement for Mg batteries has been reached with the introduction of Mg fluorinated alkoxyaluminate electrolytes. Among those, Mg[Al(hfip)₄]₂ with Coulombic efficiency over 99.5% and overpotentials below 60 mV is considered a state-of-the-art Mg electrolyte.³

In our research, we explore the field of fluorinated alkoxy electrolytes by synthesizing Mg alkoxyborates with exchanged hfip ligand for various alcohols with different sterical properties, number of binding groups, and degree of fluorination. Additionally, a synthesis of a novel Ca[Al(hfip)₄]₂ salt is developed. All electrolytes are studied by extensive physicochemical and electrochemical characterization. Our study shows that changing the anion structure allows the development of electrolytes offering improved electrochemical performance compared to the model [B(hfip)₄]₂^– – based electrolytes and exposes the most promising candidates for further studies for practical Mg and Ca rechargeable batteries.

Energy storage devices play a key role in the clean energy transition, enabling the use of energy from renewable sources and electric mobility. Although Lithium-Ion Batteries (LIBs) have several desirable characteristics (such as pollution-free operation, high efficiency, long lifetime), [1] the rapid expansion of their market has raised concerns about the availability of the raw materials used, particularly Lithium and Cobalt, with projections predicting a shortage in less than ten years. [2]

The aim of the project HYNANOSTORE - Hybrid Nanostructured Systems for Sustainable Energy Storage - recently funded by an ERC Consolidator Grant, is to revolutionize the conventional battery electrode, based on Li insertion, and develop a new architecture, in which redox organic molecules anchored to a nanostructured electrode are the active part of the battery and are able to reversibly uptake and release electrons.

The nanostructured conductive scaffold, with tailored features and an extended surface area, immobilizes redox-active molecules, facilitates charge transport, and enhances interactions between active material and electrolyte. Preliminary results are presented in order to demonstrate the working mechanism of the proposed bio-inspired engineering system, which will lead to the introduction of a new concept for the realization of economically and environmentally sustainable energy storage devices, characterized by great versatility in terms of electrode materials and electrolytes.

Rechargeable batteries that use energy-dense multivalent metals as anodes (such as magnesium and calcium) could represent a major step forward in the transition to a renewable energy economy. When combined with sustainable and pliable organic cathodes, multivalent metal batteries can realize their full potential.[1] While offering good reversibility, organic electrodes continue to underperform in multivalent electrolytes, especially in terms of achievable capacities. Therefore, to improve existing and design better organic materials for Mg and Ca batteries, a deeper understanding of their kinetic constraints must be obtained.

A major obstacle to detailed kinetic studies of organic materials in multivalent electrolytes is the lack of reliable electrochemical setups that would allow both galvanostatic cycling and electrochemical impedance spectroscopy measurements. This is a direct consequence of large overpotentials of multivalent metal anodes, which can lead to the impedance response of organic cathode being completely concealed by large anode response. A stable reference electrode for multivalent systems has yet to be found, and the use of alternative counter electrodes, such as activated carbon, sometimes introduces more problems for electrochemical characterization than it solves. Therefore, we propose the use of cyclable symmetric cells, where two organic electrodes are used, with one electrode fully charged and the other fully discharged.[2] By using a model compound poly(anthraquinonyl sulfide) we demonstrate the feasibility of the approach in lithium batteries. We further show that, in multivalent electrolytes, this type of symmetric cell allows access to the true performance of organic electrodes, by successfully eliminating counter-electrode contribution and enabling both rate capability and long-term cycling experiments. On top of that, cyclable symmetric cells allow reliable impedance measurements. We show how the impedance response differs in shape and magnitude when organic polymers interact with Li, Mg, and Ca species. Besides opening the doors for discovering the true limits of organic materials coupled with multivalent charge carriers, cyclable symmetric cells could improve the comparability of the results obtained in the field of multivalent-metal organic batteries by eliminating the role of the anode/electrolyte interface in the electrochemical tests.

Today, when a real expansion of electrode materials is happening, plenty of anode and cathode structures for alkaline-ion batteries have been developed. Mixed polyoxyanion cathode materials are becoming interesting as electrode materials for sodium-ion batteries [1]. Among them, the specific family of sodium mixed polyanionic phase, with combined phosphate and pyrophosphate units, has attracted attention as cathodes for Na-ion batteries [2]. Herein, the talk will focus on sol-gel synthesis of Fe-based mixed polyanionic phase such as Na₄Fe₃(PO₄)₂P₂O₇ and its interrelation with the secondary polyanion pyrophosphate phase (Na₂FeP₂O₇). It will be shown how the synthesis conditions control the thermal PO₄^3- - P₂O₇^4- phase transition and consequently the amount of P₂O₇^4- structural units in the synthesized powder. The special attention will be paid to assignation of phosphate/pyrophosphates vibrational modes and correlation of the polyanionic phase composition with electrochemical properties in Na-based aqueous electrolyte. Also, the difference in the electrochemical behavior of mixed polyanionic phase, between typical aqueous and water-in-salt electrolytes, will be presented and discussed in terms of new directions towards development of a new generation of more sustainable energy storage devices.    

Integrating a lithium-metal anode and a high-voltage cathode into a solid-state battery remains a formidable challenge, especially when the battery is charged beyond 4 V. Most electrolytes genuinely do not possess such a wide electrochemical stability window, but have to rely on the formation of a passivating solid electrolyte interphase, require protective electrode coatings, or have to be combined with a secondary electrolyte to achieve stable dis-/charge cycling, adding complexity.

This is also the case for prototypical polyethylene oxide-based polymer electrolytes, which form a relatively stable interface to lithium metal [1], but start oxidizing already at 3.2 V vs Li/Li⁺ via deprotonation of the terminal O-H group, as we have recently shown combining electrochemical impedance spectroscopy, infrared spectroscopy, and differential electrochemical mass spectrometry [2].

We recently employed a polymer electrolyte based on a polymerized ionic liquid to demonstrate a 4 V class solid-state battery with a lithium metal anode and a LiNi_0.8Mn_0.1Co_0.1 cathode operating at room temperature and delivering an initial capacity of 162 mAh/g and a capacity retention of 72% after 600 cycles to 4.4 V [3]. The polymer matrix consists of poly(diallyldimethylammonium) bis(fluorosulfonyl)imide (PDADMAFSI) and N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl) imide (PYR₁₃FSI) is employed as plasticizer in combination with lithium bis(fluorosulfonyl)imide (LiFSI) as lithium salt. PDADMAFSI and PYR₁₃FSI were selected because of their outstanding chemical stability and wide electrochemical stability window. Comparing to typical lithium-ion-coordinating polymer matrices, the positively charged PDADMA⁺ chains reduce lithium-ion coordination with the polymer promoting high lithium-ion mobility. LiFSI has low binding energy between Li⁺ and FSI⁻ and the ability to form stable interphases in contact with lithium metal. To confirm the high oxidative stability of this electrolyte, we also assembled a solid-state lithium-metal cell with a high-voltage spinel LiMn_1.5Ni_0.5O₄ cathode reaching an initial capacity of 132 mAh/g and a capacity retention of 76% after 300 cycles to an upper cut-off voltage of 5 V at room temperature.

The expected growth over the next few years in the battery sector is huge, with approximately 7 million tons of new batteries manufactured per year. This growth is mainly triggered by the deployment of the electric vehicle and by the energy storage coupled to wind and photovoltaic generation. However, the massive development of the sector could become an environmental problem since most commercial batteries are based on inorganic materials such as lithium, nickel and cobalt in lithium-ion batteries or vanadium in flow batteries. These materials are scarce, their production in some cases is not sustainable and some are even toxic. In this context, the replacement of these materials by organic compounds based on elements as abundant as C-H-O-N has become a very promising alternative [1].

Here I will present a wide overview of our research lines moving from organic aqueous redox flow batteries (OARFBs) to static batteries using redox-active polymer electrodes. In the case of RFBs, I will give a flavour on the multiple requirements of immiscible electrolyte including organic active species to develop a new concept of membrane-free RFB. In the second part, I will introduce the different polymer structures (linear, porous, hyperbranched, nanoparticles) containing redox active functionalities (quinones, phenazynes, etc) that we have developed in the last years. I will be focussed on their electrochemical properties in different electrolytes and their application in several battery technologies including Li-ion [2], multivalent [3], aqueous [4], all-polymer [5], etc).

A major breakthrough in chemistry and materials science has been the development of Lithium-Ion Batteries (LIBs), which show great potential for storing energy from renewable sources and as the power source for electric cars [1]. However, commercially available LIBs are based on transition metal oxide cathodes, presenting limited energy density and raising relevant environmental concerns. Organic materials have received much attention as alternative electrodes because of their high theoretical capacity, resources availability and sustainability [2,3]. In particular, Covalent Organic Frameworks (COFs), crystalline porous polymers based on organic building blocks linked by strong covalent bonds, have emerged in the past few years as promising organic electrode materials due to their high stability, high ionic conductivity and outstanding chemical and structural versatility [4]. In this presentation, I will show some different examples of redox-active COFs used as cathode materials for coin-cell type lithium batteries highlighting some of its advantages and challenges in comparison with other organic electrodes. I will also focus on the COFs processing optimization to improve the batteries performance. Finally, I will highlight some strategies to improve the charge transport in COFs, one of the main bottlenecks of these organic electrode materials [5].

Controlling and mastering electrode/electrolyte interfaces is a central goal in energy storage applications to improve the performance, the lifetime and the safety of Metal-ion batteries. This implies understanding the microscopic mechanisms taking place at these interfaces during the battery operation. The large electric fields developing at these interfaces may alter the local properties of the solvent in the vicinity of the electrode surface. To account for the potential dependence of the interface reactivity, ab initio molecular dynamic simulations or classical MD with reactive force-fields should be the appropriate methods but are still far prohibitive for the complexity of these electrochemical interface. A Grand canonical DFT approach was then develop to elucidate the mechanisms at play in these complex system. The methodology was applied to several challenging issues of electrode/electrolyte interfaces to shed light on undesired phenomena such as electrolyte degradation/ageing or metal-dendrites growth. [1,2] The perspective of this work on the development of new electrolytes for post-Li technologies and/or on the functionalization of electrode surfaces will be discussed. [3,4]

[1]
[2] A. Hagopian et al. Energy Environ. Sci., 2020, 13, 5186-5197
[3]
[4] L. H. B. Nguyen et al. Phys. Chem. Chem. Phys. 2022 Accepted

Renewable energy production is characterized by intermittent power output and requires large-scale applications to improve energy storage capability (currently, less than 1% of the electrical energy production can be stored). Developing low-cost and environmentally friendly electrochemical storage systems characterized by high performance is of fundamental importance for a sustainable energy economy. The currently most mature battery technology is the lithium-ion battery, considered one of the most appealing candidates as a power source for electric vehicle applications. However, the large-scale application of lithium-ion batteries is currently under discussion due to the limited lithium and certain transition metals such as Co and Ni resources. Several other metallic anodic materials such as sodium, potassium, calcium, magnesium and aluminium [1-3], characterized by a higher abundance of lithium, have been considered suitable candidates for electrochemical storage devices in replacing lithium systems. Notably, significant efforts are being devoted to understanding and addressing key challenges in developing these so-called “beyond Li-ion” chemistries, and substantial insights into their storage and failure mechanisms have been obtained over the past few years thanks to advanced characterization and computation/modelling techniques. An overview of our activity in “beyond Li-ion” batteries field and an evaluation of the capability of this technology will be presented. [4–8]

References

[1]           G. A. Elia, K. Marquardt, K. Hoeppner, S. Fantini, R. Lin, E. Knipping, W. Peters, J.-F. Drillet, S. Passerini, R. Hahn, Adv. Mater. 2016, 28, 7564.

[2]           G. A. Elia, K. V Kravchyk, M. V Kovalenko, J. Chacón, A. Holland, R. G. A. Wills, J. Power Sources 2021, 481, 228870.

[3]           G. G. Eshetu, G. A. Elia, M. Armand, M. Forsyth, S. Komaba, T. Rojo, S. Passerini, Adv. Energy Mater. 2020, 10, DOI 10.1002/aenm.202000093.

[4]           F. Colò, F. Bella, J. R. Nair, C. Gerbaldi, J. Power Sources 2017, 365, 293.

[5]           G. A. Elia, G. Greco, P. H. Kamm, F. García‐Moreno, S. Raoux, R. Hahn, Adv. Funct. Mater. 2020, 30, 2003913.

[6]           X. Liu, G. A. Elia, S. Passerini, J. Power Sources Adv. 2020, 2, 100008.

[7]           X. Liu, H. Euchner, M. Zarrabeitia, X. Gao, G. A. Elia, A. Groß, S. Passerini, ACS Energy Lett. 2020, DOI 10.1021/acsenergylett.0c01767.

[8]           X. Liu, G. A. Elia, B. Qin, H. Zhang, P. Ruschhaupt, S. Fang, A. Varzi, S. Passerini, ACS Energy Lett. 2019, DOI 10.1021/acsenergylett.9b01675.

All-solid-state lithium metal batteries (ASSLMBs) with sulfide-based solid electrolytes with high ionic conductivity are regarded as the ultimate next-generation energy storage systems due to their enhanced safety and energy density by enabling the use of metallic anodes. Li metal is considered the holy grail anode material because of its high theoretical specific capacity (3860 mAh/g) and the lowest electrochemical potential (-3.06 V versus standard hydrogen electrode). However, its practical use has been hindered by several issues related to the interface, such as contact loss during cycling, which accelerates Li dendrite growth, and chemical instability between Li metal and sulfide-based solid electrolyte. To construct safe and high energy density ASSLBs, understanding the degradation mechanism of the ASSLBs is imperative. In this talk, the fundamental degradation mechanisms of the ASSLMBs underlying electrochemical and mechanical aspects are introduced first. Subsequently, we briefly review the current research on the ASSLMSs. Finally, this presentation introduces our strategies for developing high-performance ASSLMBs by stabilizing the Li metal and sulfide-based solid electrolytes interface. The designed ASSLMBs could effectively retard the Li dendrite growth and unwanted side reaction and shows much enhanced electrochemical performance.

The transformation from liquid- to solid-state architecture is expected to improve safety, fabrication, and temperature stability of energy storage devices, particularly if constraints of low ionic conductivity, low cation transport properties and stringent processing conditions are overcome [1].

Here, an overview is offered of the recent developments in our labs on innovative polymer-based electrolytes allowing high ionic mobility, particularly attractive for Li-metal batteries, and obtained by different techniques, including solvent-free UV-induced photopolymerization. Electrochemical performances in lab-scale devices can be readily improved using different kind of RTILs or other specific low-volatile additives. Cyclic voltammetry and galvanostatic charge/discharge cycling coupled with electrochemical impedance spectroscopy exploiting different electrode materials (e.g., LFP, Li-rich NMC, Si/C) demonstrate specific capacities approaching theoretical values even at high C-rates and stable operation for hundreds of cycles at ambient temperature [2,3]. Direct polymerization procedures on top of the electrode films are also used to obtain an intimate electrode/electrolyte interface and full active material utilization in both half and full cell architectures. In addition, results of composite hybrid polymer electrolytes, as well as new single-ion conducting polymers are shown [4,5], which are specifically developed to attain improved ion transport and high oxidation stability for safe operation with high voltage electrodes even at ambient conditions.

The rapid technological evolution and population growth demand more sustainable materials compatible with the circular economy paradigm. Natural polymers, a class of materials produced by biological and renewable resources, represent an important oportunity for the development of more sustainable technologies for their application in energy storage systems in general and batteries in particular [1].

Silk fibroin (SF), obtained from Bombyx mori silkworm cocoons, carrageenan, that are sulphated polysaccharides that occur as matrix material in several species of red seaweeds of the class Rhodophyceae and poly(L-lactic acid) (PLLA), an enantiomeric polyester produced from lactic acid synthesis are one of those materials due to their mechanical and thermal properties, non-toxicity biodegradability and biocompatibility.

In order to improve the battery performance it is usual to add different inorganic fillers to the polymeric separators. Metal-organic frameworks (MOFs) are a class of porous crystalline solids that impregnated with ionic liquids (ILs) can substantially improve the conductivity values of the separator [2].

The present work presents the development of separator membranes for lithium-ion batteries (LIBs) applications based on those natural polymers and preliminary results based on the MOF-74 impregnated with the [EMIm][TFSI] ionic liquid.

The samples were evaluated in terms of morphology, physical-chemical characteristics, thermal behavior, mechanical and electric and ionic proprieties in order to evaluate their applicability for separator membranes in LIBs. The half-cells prepared with silk fibroin, carrageenan and  poly(L-lactic acid) show good cyclability and a discharge capacity of 131,1 mAh.g^-1 at C/8-rate, 145 mAh.g^-1 at C/10-rate and 93 mAh.g^-1 at 1C-rate, respectivelly,  demonstrating excellent battery performance.

Cobalt is a key material for the production of Li-ion batteries. Today already more than 60% of mined cobalt is destinated for battery cathodes. Additionally, 60% of the worldwide cobalt resources are in the politically unstable Congo (DRC) and are extracted in many cases by child labour that implies an ethical and health concern due to its toxicity[1]. LiNi_1.5Mn_0.5O₄ spinels are between the most promising alternatives as they present a long high voltage plateau, very fast lithium insertion and extraction, which yield to high energy densities of 650 Wh/kg at cell level (vs the cathode mass). However, among the main challenges of these batteries, are the oxidation stability of the electrolyte when cycling at high voltage and the cycle life when practical electrode loadings are employed [2,3]. Within the CoFBAT project, gel electrodes and electrolytes based on the new Solef® PVdF copolymer have been developed. The current results at full cell level shows over 250 cycles up to 80% state of health when the LNMO cathode electrode is jellified. Still a ten-fold increase of the cycle life is needed to outperform commercial Li-ion batteries. For better understanding the degradation mechanisms of these batteries, new post-mortem protocols for gel-based Li-ion batteries need to be developed. The use of gel-based electrodes and electrolytes difficult the disassembly and characterization process, especially the analysis of the solid-electrolyte interphases. In this work we summarized the main challenges of LNMO to outperform current commercial Li-ion batteries as well as strategies proposed to overcome them. Finally, we present a multi-technique approach for the post-mortem analysis of gel-based Li-ion batteries that allow to identify the main driving source of capacity fade.

High-throughput approaches in computational materials discovery often yield a combinatorial explosion that makes the exhaustive rendering of complete structural and chemical spaces impractical. A common bottleneck when screening new compounds with archetypal crystal structures is the lack of fast and reliable decision-making schemes to quantitatively classify the computed candidates as inliers or outliers (too distorted structures). Machine learning-aided workflows can solve this problem and make geometrical optimization procedures more efficient. However, for this to occur, there is still a lack of appropriate combinations of suitable geometrical descriptors and accurate unsupervised models which are capable of accurately differentiating between systems with subtle structural changes. Here, considering as a case study the compositional screening of cubic Li-argyrodites solid electrolytes, we tackle this problem head on. We find that Steinhardt order parameters are very accurate descriptors of the cubic argyrodite structure to train a range of common unsupervised outlier detection models. And, most importantly, the approach enables us to automatically classify crystal structures with uncertainty control. The resulting models can then be used to screen computed structures with respect to an user-defined error threshold and discard too distorted structures during geometrical optimization procedures. Implemented as a decision node in computer-aided materials discovery workflows, this approach can be employed to perform autonomous high-throughput screening methods and make the use of computational and data storage resources more efficient.

Recent advances in wearable and IoT technologies has led to a strong demand for embedded Li-ion microbatteries. There is also a need for microbatteries with superior mechanical characteristics such as flexibility, stretchability while maintaining strong electrochemical performances.

In this work, we present micro/nano-structuration of microbatteries electrodes surface [1]. Patterning of electrodes materials allows improvement of both mechanical resistance and electrochemical performance of these microbatteries [2]. 3D surface enhancement owing to the design of micropillar electrodes permits to fulfil this need. Lithium nickel manganese oxide (positive electrode) and Lithium titanate oxide (negative electrode) micropillars with different sizes are fabricated on aluminium foils by laser ablation technique and are then separated by a polymer electrolyte to form flexible lithium-ion microbatteries [3].

We have demonstrated that the micropillar size has an influence on the electrochemical performance of Li-ion microbatteries. Optimized pillar dimensions drastically enhance areal capacity. For micropillar size of 25 µm*25 µm the areal capacity is 822 μAh.cm^–2 at 1C (1×2 cm electrodes) [4].

In addition, a treatment of electrolyte-coated electrodes under vacuum improves electrochemical properties due to a better filling of the interpillar space by the electrolyte polymer. Under optimized conditions, the capacity delivered by the microbattery is four times higher than the planar system counterpart. Higher areal discharge capacity is obtained when the electrodes follow a treatment in vacuum: 1049 μAh.cm^–2 at 1C for micropillar size of 25 µm*25 µm. This vacuum treatment can be easily done at room temperature. Figure 1 shows the increase of areal capacity at 1C versus the time vacuum treatment.

Thanks to low thickness below 1 mm and high flexibility, these optimized microbatteries can be used in applications such as powering smart contact lens [5].