Towards Massless energy storage

Structural battery composites belong to a type of multifunctional materials that offer massless energy storage in electric vehicles and electric tools, as illustrated in Figure 1. In the paper Three-dimensional reconstruction and computational analysis of a structural battery composite electrolyte, recently published in Communications Materials, we study the three-dimensional structure of a porous structural battery electrolyte and relates it to the multifunctional performance of the material. The structural battery electrolyte (SBE) is a key constituent in structural batteries with the role to transport lithium ions between the electrodes and to transfer mechanical loads between fibres in these electrodes.

Figure 1. Massless energy storage. A schematic illustration of the structural battery and its application for massless energy storage. Illustration by Yen Strandqvist, Chalmers University of Technology.

 The SBE is a material consisting of a porous glassy polymer where the pores are occupied by a liquid electrolyte, as illustrated in Figure 2a.  Reliable analysis of the SBE’s multifunctional properties require detailed description of its three-dimensional structural. For this purpose, we use combined focused ion beam and scanning electron microscopy to generate 3D models of the SBE material as illustrated in Figure 2b. These models are transferred into finite element models to assess the SBE concerning its elastic modulus and ionic conductivity. Characterization of the three-dimensional structure also provides information on the diameter and volume distributions of the polymer and pores, as well as geodesic tortuosity, i.e., the distance the ions need to travel.

Figure 2. The structural battery electrolyte. a) A schematic illustration of the structural battery and the SBE. b)  FIB-SEM micrographs stacked and reconstructed into a 3D material model for analysis. Illustration by Shanghong Duan, Chalmers University of Technology.

 The results reveal that elastic modulus can be accurately predicted, whereas ionic conductivity is overestimated by the FE models. The geometry and dimensions of the polymer backbone and pores are reported. Finally, the distance the Li-ions have to travel is 80% further than the distance between the electrode due to the tortuosity of the porous network.

 The study is a collaboration between Chalmers University of Technology and KTH, the Royal Institute of Technology, both in Sweden, and TU Braunschweig in Germany. The paper is authored by Shanghong Duan, Martina Cattaruzza, Vinh Tu, Robert M. Auenhammer, Ralf Jänicke, Mats K.G. Johansson, Fang Liu, and Leif E. Asp