• Energy Research

Surfaces of active materials are understood to play an important role in the performance and lifetime of lithium-ion batteries, but they remain poorly characterized and therefore cannot yet be systematically designed.

Tortuosity values of porous battery electrodes determined using electrochemical impedance spectroscopy in symmetric cells with a non-intercalating electrolyte are typically higher than those values based on numerical analysis of 3D tomographic reconstructions. The electrochemical approach assumes that the electronic resistance in the porous coating is negligible and that the tortuosity of the porous electrode can be calculated from the ionic resistance determined by fitting a transmission line equivalent circuit model to the experimental data. In this work, we validate the assumptions behind the electrochemical approach. First, we experimentally and theoretically investigate the influence of the electronic resistance of the porous electrode on the extracted ionic resistances using a general transmission line model, and provide a convenient method to determine whether the electronic resistance is sufficiently low for the model to be correctly applied. Second, using a macroscopic setup with known tortuosity, we prove that the ionic resistance quantified by the transmission line model indeed yields the true tortuosity of a porous medium. Based on our findings, we analyze the tortuosities of porous electrodes using both X-ray tomography and electrochemical impedance spectroscopy on electrodes from the same coating and conclude that the distribution of the polymeric binder phase, which is not imaged in most tomographic experiments, is a key reason for the underestimated tortuosity values calculated from 3D reconstructions of electrode microstructures. Journal of the Electrochemical Society, 165 (3) ISSN:0013-4651 ISSN:1945-7111

Pore space connectivity is a useful metric for describing microstructure of lithium ion battery components.

The transition from liquid organic electrolytes to solid-state electrolytes promises safer and more energy-dense lithium ion batteries. Although this technology has been demonstrated, the question of how to manufacture solid-state batteries at the cost and scales needed to be competitive remains. Here we propose and demonstrate curtain coating as a method for manufacturing composite solid-state electrolytes in roll-to-roll processes at web-speeds of over 80 m/min. The method is compatible with existing lithium-ion battery electrode manufacturing lines and is able to produce uniform electrolyte films with thicknesses below 15 micrometers. iScience, 24 (2) ISSN:2589-0042

The ability to engineer electrode microstructures to increase power and energy densities is critical to the development of high-energy density lithium-ion batteries. Because high tortuosities in porous electrodes are linked to lower delivered energy and power densities, in this paper, we experimentally and computationally study tortuosity and consider possible approaches to decrease it. We investigate the effect of electrode processing on the tortuosity of in-house fabricated porous electrodes, using three-dimensionally reconstructed microstructures obtained by synchrotron x-ray tomography. Computer-generated electrodes are used to understand the experimental findings and assess the impact of particle size distribution and particle packing on tortuosity and reactive area density. We highlight the limitations and tradeoffs of reducing tortuosity and develop a practical set of guidelines for active material manufacture and electrode preparation.

Abstract Li-S batteries with an improved cycle life of over one thousand cycles have been achieved using cathodes of sulfur-infiltrated nanoporous carbon with carbonate-based electrolytes. In these cells, a protective cathode-electrolyte-interphase (CEI) is formed, leading to solid-state conversion of S to Li2S in the nanopores. This prevents the dissolution of polysulfides and slows capacity fade. However, there is currently little understanding of what limits the capacity and rate performance of these Li-S batteries. Here, we aim to deepen the understanding of the capacity and rate limitation using a variety of structure-sensitive and electrochemical techniques, such as operando small angle neutron scattering (SANS), operando X-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS), and galvanostatic charge/discharge. Operando SANS and XRD give direct evidence of CEI formation and solid-state sulfur conversion occurring inside the nanopores. Electrochemical measurements using two nanoporous carbons with different pore sizes suggest that charge transfer at the active material interfaces and the specific CEI/active materials structure in the nanopores play the dominant role in defining capacity and rate performance. This work helps defining strategies to increase the sulfur loading while maximizing sulfur usage, rate performance, and cycle life.

Nature Energy, 4 (1) ISSN:2058-7546