Semi-Interpenetrating Networks for All-Solid-State Lithium Metal Batteries

Abstract

In the past two decades, exponentially growing markets of mobile consumer electronics and electric vehicles caused an increasing demand towards higher energy and power density in energy storage technologies. Aiming to overcome the intrinsic limitations of state of the art liquid organic carbonate-based electrolytes with regard to higher energy densities and cost efficient cells solid state electrolytes are a promising topic of research. Enabling not only the use of electrolyte layers in the range of a few micrometers and a reduction of needed security features of the cell housing, but also the utilization of lithium metal as anode. Besides the prominent classes of oxidic ceramic and sulfidic glassy electrolytes, the class of lithium ion conducting polymer electrolytes comprises a large variety of different subclasses. The subclass of semi-interpenetrating networks (s-IPNs) defines a combination of at least two polymer networks penetrating each other without a covalent bonding between the different polymer species. Thanks to its excellent interface wetting ability, processability and lithium metal compatibility, polyethylene oxide (PEO) was selected as lithium ion conducting polymer.[1] This combination of different polymer types allows the tailoring of vital physicochemical and electrochemical properties of the resulting s-IPN membranes. Possible benefits of a second interwoven polymer matrix refer to the reduction/suppression of PEO crystallization inside of confinements, thus allowing the utilization of polymer membranes at ambient temperature, an enhanced mechanical stability of thin film membranes compared to single polymer materials and the improved homogeneity of lithium precipitation by a more defined interface structure.[2] Depending on the preparation route of the s-IPN, not only the polymer itself but also the polymer interfaces can be tuned selectively by introduction of, for example, highly hydrophobic substances like siloxanes, which tend to accumulate at the membrane surfaces.[3] The prepared s-IPN membranes in this work were investigated by means of selected thermal, electrochemical and spectroscopy techniques including differential scanning calorimetry, galvanostatic and potentiostatic experiments as well as impedance spectroscopy. This work aims for an economic approach to tailor vital physicochemical properties of s-IPN electrolyte membranes by utilization of PEO as lithium ion conductor and lithium metal as anode material using a single-step solution casting synthesis route towards advanced all-solid-state lithium metal batteries.