Effect of Microstructure on the Ionic Conductivity of an All Solid-State Battery Electrode

Abstract

In literature, the ionic conductivity of solid electrolytes is often discussed as one of the most important properties of an all solid-state battery. However, the behavior of the electrolyte inside a composite electrode and the influence of electrode structure on the ionic conductivity is neglected in most of the studies. In this work we manufactured model electrodes with clearly defined structures by using electrochemically inert glass particles as model active material with six different volume fractions and four different particle sizes, respectively. Higher volume fractions and smaller particles led to a decrease of ionic conductivity down to two decades due to emerging pores and a rise of tortuosity. Beneath the ionic conductivity the interface resistance between Li-metal and model electrodes was investigated, clearly indicating that high volume fractions of small active materials led to higher interface resistances. Finally, a model is introduced to predict the effective ionic conductivity of a solid electrolyte within an all solid-state battery electrode by just knowing the volume fraction of active material.

Modeling the Electrical Conductive Paths within All‐Solid‐State Battery Electrodes

“…The method is able to reproduce the increment and further consolidation of the electrical conductivity in dependence on the CB content, enabling its use for further investigations on electrode morphology and additional applications. Moreover, the tortuosity of the simulated electrodes is numerically calculated and the ionic conductivity is derived according to . In fact, bearing in mind the gained outcomes, it is not advisable to increase the amount of CB above 5 wt %, due to the almost discernible increase in electrical conductivity and consequent hindering of ionic diffusion.…”

“…Finally, a calendering step was carried out via a laboratory calender device (Saueressig GmbH) with a roll temperature of 90 °C and a roll speed of 0.1 m min −1 to reach the targeted electrode thickness of 60 mm. The electrode mass was determined with a laboratory scale and the thickness with an indicating gauge (Mitutoyo, Planolith, ID‐C112AXB); both are required to calculate the porosity of the electrodes according to Froboese et al . The electrical conductivity measurements were performed via a two‐point approach with a material testing machine (Z020; Zwick GmbH & Co. KG).…”

“…Taking this into consideration, the porosity was substituted in Eq. by the volume fraction of the electrolyte, an approach that has already been successfully taken in . The electrolyte diffusion coefficient equals 2 × 10 −4 S cm −1 , as reported by Pesko et al .…”

“…Nevertheless, little research has been conducted on these properties within the context of ASSB, so far. One of the few works has dealt with the ionic conductivity of the solid electrolyte, demonstrating the influence of various ASSB electrode structures on this parameter . Hou et al confirmed the major significance of interconnected electronic pathways in the electrochemical performance of a lithium‐sulfur ASSB and experimentally verified the equal relevance of electron conduction in comparison to ion transfer.…”

Fundamentals of Electrolytes for Solid-State Batteries: Challenges and Perspectives

“…Although many efforts have been made to overcome the chemo-mechanical challenges, the issues caused by the SSE matrix complex and electrode manufacture remain uncovered, which inhibits the large-scale application of SSBs (Kato et al, 2018). Apart from the critical electrode-electrolyte interface, the inevitable voids in the SSE matrix not only reduce the lithium diffusion paths in the SSE but also provide space for lithium dendrite integration (Froboese et al, 2019). Therefore, developing dense electrolyte and electrode with fewer spaces has become another critical approach.…”