Solid-state batteries are a promising new technology that could revolutionize lithium-ion technology. There are a few differences to consider when selecting a solid electrolyte. While ceramic electrolytes have comparatively good ionic conductivity and are stable electrochemically and mechanically, their surface properties leave much to be desired. Since they are very hard and immobile, contact with the electrodes often only consists of point contacts and not continuous surfaces. Polymer electrolytes, on the other hand, are soft and flexible, leading to suitable contact surfaces. Since they become liquid at high temperatures, they are also easier to process. On the other hand, the ionic conductivity is generally much lower than that of ceramic electrolytes. One approach to use the favorable properties of both electrolytes is to combine polymer and ceramic electrolytes in one cell.

One way to achieve this and, at the same time, minimize the disadvantages of both electrolytes is to use structured cathodes. This work shows a basic structure made of porous ceramic with embedded grooves, based on the work of Scheller et al., 2024. These grooves and the pores opened up by them are then filled with a mixture of polymer electrolyte, active material and conductive carbon black. The polymer electrolyte ensures good contact with the active material, while the ceramic ensures low-resistance transport to the anode. The structuring makes minimizing the path in the poorly conductive polymer possible.

Using a pseudo-3D Doyle-Fuller-Newman model, this work shows how a cell with such a structured composite cathode would perform during a charge with 1 C. The cathode lithium deintercalation starts at the area nearest to the anode, where the path through the polymer is the smallest. Once the OCV in this area rises, the deintercalation reaction will disperse backward, changing the current distribution in the process. This, in turn, will have an impact on the cell’s overpotential. The deintercalation reaction dispersing over a wider area will lead to a drop in charge transfer overpotential. If, like in this example, the 2D structure is triangular shaped, with its tip toward the anode, the changing current path will also lead to a drop-in overpotential within the polymer and at the polymer-ceramic boundary. Resulting in an overall diminishing overpotential over time. The general trend of the diminishing overpotential over time will then finally be overlaid with some noise resulting from the nonlinear open circuit voltage function of the active material.