The investigation of thin-film battery materials is essential for the development of future technologies capable of enabling highly miniaturized energy storage systems for critical applications, such as compact electronics, medical implants, and the Internet of Things (IoT). Thin layers also serve as exceptional model systems for gaining a fundamental understanding of diffusion phenomena within bulk materials and across interfaces. Due to their simple geometry and versatility, these thin films enable the creation of synthetic systems that can be representative of large-scale battery architectures.

In this work, we present several examples where thin films are utilized in combination with non-destructive optical techniques to provide insights into material changes during operation. Specifically, this study highlights the potential of operando spectroscopic ellipsometry and Tip-Enhanced Raman Spectroscopy for the real-time investigation of cathode materials.

Beyond their use as model systems, significant efforts over the past decades have been directed toward extending this approach to real devices. To date, one of the few commercially successful thin-film energy storage devices is the lithium solid-state battery (SSB) that incorporates a lithium phosphorus oxynitride (LiPON) electrolyte. Among alternative ceramic electrolytes, the NASICON-type superionic conductor Li₁₊ₓAlₓTi₂₋ₓ(PO₄)₃ (LATP) is particularly promising due to its high ionic conductivity (approximately 1 mS·cm⁻¹) and its stability in ambient air at elevated temperatures.

In this talk, we will discuss our recent progress in the integration of thin films into ceramic SSBs and the development of novel tools for materials research and device implementation. To achieve this, LATP[1] and various electrode materials were deposited using Large-Area Pulsed Laser Deposition. Spinel-type LiMn₂O₄[2] and Li₄Ti₅O₁₂[3], as well as olivine-type LiFePO₄, were selected due to their excellent stability, low cost, and environmental compatibility. Bi-layers consisting of LATP and these electrode materials were fabricated to investigate the structure and properties of their interfaces.

The development of thick, high-loading electrodes is essential to increase the energy density and reduce the cost of next-generation solid-state batteries (SSBs). In this work, we explore advanced ceramic shaping techniques, such as Powder Injection Moulding (PIM), Powder Extrusion Moulding (PEM), and Fused Filament Fabrication (FFF), to fabricate additive-free thick electrodes based on commercial and available ceramic active powders, such as Li₄Ti₅O₁₂ (LTO), LiFePO₄, LiCoO₂, NMC, NCA. These shaping routes allow the fabrication of robust, binder-free electrodes with precisely controlled geometries and high mass loadings (>100 mg·cm⁻²), while maintaining mechanical integrity and suitable porosity for ionic and electronic transport [1, 2, 3].

The feedstocks are formulated using thermoplastic binders and optimized through rheological studies to ensure homogeneous dispersion and extrusion behaviour. After shaping, debinding and sintering steps yield robust ceramic structures with thicknesses up to 300-500 μm and open porosities in the 20–30% range. Electrochemical testing in half- and full-cell configurations confirms excellent cycling stability and demonstrates high areal and volumetric capacities—>15 mAh·cm⁻² and >315 mAh·cm⁻³ for 500 μm electrodes fabricated via PEM, and 25 mAh·cm⁻² and 400 mAh·cm⁻³ for 650 μm electrodes fabricated by PIM [1,4]. Notably, the use of FFF enables the fabrication of electrodes with even greater thicknesses (~800 μm) and ultra-high mass loadings (285 mg·cm⁻²), achieving outstanding areal and volumetric capacities of 28 mAh·cm⁻² and 354 mAh·cm⁻³, respectively [5]. The scalable and versatile nature of these ceramic shaping techniques paves the way for the integration of structured and 3D-architectured electrodes in advanced SSB architectures.

Overall, our results demonstrate that ceramic forming technologies originally developed for structural ceramics can be successfully adapted to the fabrication of electrochemical devices, offering an effective route toward compact, high-performance solid-state batteries.

The transition from conventional lithium-ion batteries to all-solid-state batteries (ASSBs) is currently at the forefront of energy storage research. A critical component in this shift is the development of efficient solid-state electrolytes (SSEs), particularly ceramic-based ones, which combine high ionic conductivity with the mechanical strength needed to mitigate dendrite growth. Among these, lithium aluminium titanium phosphate (LATP) stands out due to its high bulk ionic conductivity (~3 mS cm^-1) and chemical stability under ambient conditions. However, the fabrication of LATP typically requires high sintering temperatures (>1000 ºC), limiting its scalability and integration with other battery components.

To overcome this challenge, dense LATP SSEs are produced at significantly reduced temperatures (~150 ºC) using the Cold Sintering Process (CSP). A key feature of this research is the use of in operando Electrochemical Impedance Spectroscopy (EIS) as a real-time monitoring tool during the sintering process. To enable this, a novel in operando EIS setup was specifically designed and implemented for this purpose.

Through this setup, several critical parameters influencing the CSP process and the final electrochemical properties of the LATP SSEs have been systematically investigated:

1. Optimization of Transient Liquid Phase (TLP) content, to achieve the best balance between densification and ionic conductivity.
2. Tailoring Bi₂O₃ additive concentration, which acts as a sintering aid, enhancing both microstructure and electrochemical performance.
3. Control of starting LATP particle size, to balance densification and ionic transport properties.
4. Chemical engineering of intergranular phases by introducing a LiOH:LiNO₃ eutectic mixture, enabling further tuning of the grain boundary properties.
5. Analysis of key process variables, such as pressure, dwell time, and heating profile, which directly influence the sintering mechanism and the resulting microstructure.

The combination of low-temperature CSP and in operando EIS monitoring has proven to be a powerful approach for understanding and controlling the complex interplay between processing conditions, microstructure evolution, and electrochemical performance. The methodology developed here not only provides fundamental insights into the densification mechanisms at play but also opens new routes for the scalable fabrication of high-performance SSEs for next-generation ASSBs.

The development of sustainable battery technologies requires not only the replacement of critical raw materials but also the elimination of hazardous components used in electrode fabrication. In this context, bio-based binders [1] and novel frameworks [2] have emerged as promising alternatives to conventional materials that rely on fluorinated compounds and toxic solvents. Recent efforts focus on integrating environmentally friendly polymers with innovative porous materials to produce electrodes through water-based processes. Such combinations can enhance structural stability [3,4], reduce harmful emissions, and improve electrochemical performance by promoting favourable interactions at the electrode–electrolyte interface. This study explores the synergy between natural binders and advanced framework structures for lithium-ion batteries, emphasizing the potential to replace conventional fluorinated binders while maintaining high capacity and cycling stability. The findings highlight the importance of green synthesis routes, abundant precursors, and multifunctional components in advancing next-generation electrodes with lower environmental impact, contributing to more sustainable energy storage solutions aligned with circular economy principles.

Composite Solid Electrolytes (CSEs) are emerging as safer and more efficient alternatives to liquid electrolytes, playing a crucial role in the development of lithium- and sodium-based All-Solid-State Batteries (ASSBs). In this context, our research group has focused on enabling the co-processing of ceramics, polymers, and ionic salts at low temperatures through the Cold Sintering Process (CSP). CSP is an innovative technique that reduces the sintering temperature of ceramics by nearly 1000 °C compared to conventional, energy-intensive methods.

This low-temperature strategy not only allows the incorporation of polymeric components—thus combining the mechanical and electrochemical benefits of both ceramics and polymers—but also significantly cuts energy consumption and associated CO₂ emissions. The resulting hybrid electrolytes exhibit enhanced structural and electrochemical properties, making CSP a promising route for next-generation solid-state systems. Furthermore, CSP enables the direct co-sintering of bilayered configurations, such as electrolyte–electrode assemblies, simplifying device architecture.

In this contribution, we will highlight the key parameters that govern the fabrication of competitive CSEs and bilayered structures via CSP, while addressing the critical challenges that must be tackled to enable the widespread implementation of ASSBs.

The development of sulfide-based lithium superionic conductors (>10⁻⁴ S cm⁻¹) has addressed the challenge of low ionic conductivity in the solid state, spurring the development of all-solid-state batteries (ASSB) over the past decade [1]. Despite the suitable ionic conductivity of sulfide-based materials, they can be challenging to handle due to interfacial instability against active materials (electrodes and conductive binder) within the cell. The limited electrochemical window of sulfide solid electrolytes (of ca. 2–3 V vs. Li/Li⁺) can trigger chemical and electrochemical decomposition within the cell that leads to limited cell life. Herein Raman microscopy is demonstrated as a powerful analytical tool to monitor interfacial changes (both ex situ and operando) on electrodes containing a variety of solid electrolytes (β-Li₃PS₄, Li₆PS₅Cl, Li₇Si₂S₇I and Li₁₀GeP₂S₁₂) [2-4]. Furthermore, Raman microscopy was used to map the distribution of degradation products with the composite electrode, before and after cycling and highlighted degradation at sulfide electrolyte/conductive carbon/binder interface.

Li-ion batteries are presently the technology of choice to power electric vehicles and portable electronic devices. This great success is also the result of the development of high-performance liquid organic electrolytes providing a high ionic conductivity and wide electrochemical stability. When targeting a further improved safety, however, solid-state electrolytes are anticipated to provide significant advantages owing to their commonly higher thermal stability and reduced flammability in combination with an inhibited leakage issue – especially when transitioning from classic graphite-based anodes to high-capacity alternatives such as silicon or lithium metal. Nonetheless, all solid electrolyte systems come with their own challenges, which are, though, frequently complementary. Thus, there is a tremendous interest in smartly combining different electrolyte classes to finally achieve a real breakthrough towards safer high-energy and high-performance lithium batteries.

Herein, several different composite (frequently referred to as “hybrid”) electrolyte systems will be presented, starting from the reasoning for the given design and selection of components, highlighting the potential and eventual benefits and remaining challenges, and finally discussing some very recent in-depth insights into the charge transfer across the different phase boundaries, which are essential for the meaningful design of such multiphase systems.