A major challenge in solid-state batteries is electrochemical degradation at the electrode-electrolyte interface, especially when using high-energy cathode materials such as LiNi_1−x−yCo_xMn_yO₂ (NCM) or silicon anodes, along with sulfide-based electrolytes such as Li₆PS₅Cl. The unstable interface leads to capacity fading during cycling. To address this, research is focusing on three parts: (a) to create reliable coating methods to obtain uniform coatings on NCM and silicon particles; (b) to explore novel polymer coatings to improve the performance of NCM and silicon in solid-state batteries, aiming to enhance cycling stability; (c) to examine the role of polymer coatings in solid-state batteries, providing direction for future polymer coating designs.

This research aims to enhance the areal capacity of solid-state lithium batteries in pouch cell format. The cathode plays a critical role, housing both the cathode active material (CAM) and solid electrolyte (SE), which are essential for energy storage. Although high loading and high weight fractions of CAM to thiophosphate-based SEs are theoretically expected to boost energy density, the opposite often occurs due to inefficient interfacial connectivity between CAM and SE, resulting in increased tortuosity of lithium-ion transportation. This issue is addressed by optimizing the microstructure of dry-processed, polymer-coated cathodes. Additionally, the integration of current collectors and electrodes with polymeric binders is investigated to strengthen adhesion between these components.

A major challenge in the development of solid-state batteries is the stabilization of the interface between the lithium metal anode and the solid electrolyte. This solid-solid interface is a challenge to maintain during cycling if only inorganic materials are used. While sulfide-based solid electrolytes have the highest ionic conductivities, they suffer from poor electrochemical stability in contact with lithium metal, leading to solid electrolyte interphase formation. Dendrite formation during lithium plating and pore formation during stripping are two further failure mechanisms. To mitigate these issues, a protective polymer coating is developed for the lithium metal anode, which may prevent dendrites and promote homogenous lithium plating.

This research aims to enhance the capacity and cycling stability of cathode active materials in sodium solid-state batteries. In these batteries, cathode materials such as transition metal oxides (TMOs) encounter significant challenges during cycling. The electrochemical interaction between TMOs and solid electrolytes such as sulfides, often leads to detrimental side reactions, resulting in the formation of substantial quantities of decomposed electrolyte byproducts, cracking of cathode particles, and loss of interfacial contact. Furthermore, the larger ionic radius of Na⁺ compared to Li⁺ exacerbates volume expansion, further compromising the cycling stability of oxide materials. These combined electro-chemo-mechanical challenges can be mitigated through the application of protective coatings on the TMOs and the implementation of optimal pressure conditions.

To address the challenges of poor contact and low ionic conductivity in solid electrolytes (SEs) and polymer electrolytes (PEs), a hybrid approach is under investigation, with the intention of combining the advantages of both electrolyte types. Incorporating SEs and PEs together in batteries introduces new interfaces, which can lead to additional potential drops. Therefore, a comprehensive understanding of these interfaces is crucial for selecting optimal electrolyte combinations to enhance battery performance. In the MiNaBatt project, we aim to perform detailed (electro-)chemical analysis of the SE/PE interface to identify the key factors influencing the interface resistance under various conditions, such as different currents and temperatures. To achieve this, multiple-electrode pouch cells are fabricated, and electrochemical testing is conducted using various SE and PE combinations.