Influence of electrochemical cycling on the rheo-impedance of anolytes for Li-based Semi Solid Flow Batteries

Latest progress and challenges associated with lithium-ion semi-solid flow batteries: a critical review

Since the proposal of the concept of semi-solid flow batteries (SSFBs), SSFBs have gained increased attention as an alternative for large-scale energy storage applications. As a new type of high energy density flow battery system, lithium-ion semi-solid flow batteries (Li-SSFBs) combine the features of both flow batteries and lithium-ion batteries and show the advantages of decoupling power and capacity. Moreover, Li-SSFBs typically can achieve much higher energy density while maintaining a lower cost. Therefore, Li-SSFBs are some of the most promising technologies for future energy storage. Despite these advantages, a significant gap towards the commercialization of Li-SSFBs still exists. In this article, we have reviewed the research progress of Li-SSFBs in aqueous and non-aqueous systems in recent years. We have further discussed the future research trends and application prospects of Li-SSFBs, providing guidelines for future research in this area.

Quantifying the hydrodynamic contribution to electrical transport in non-Brownian suspensions

Electrical transport in semiconducting and metallic particle suspensions is an enabling feature of emerging grid-scale battery technologies. Although the physics of the transport process plays a key role in these technologies, no universal framework has yet emerged. Here, we examine the important contribution of shear flow to the electrical transport of non-Brownian suspensions. We find that these suspensions exhibit a strong dependence of the transport rate on the particle volume fraction and applied shear rate, which enables the conductivity to be dynamically changed by over 10⁷ decades based on the applied shear rate. We combine experiments and simulations to conclude that the transport process relies on a combination of charge and particle diffusion with a rate that can be predicted using a quantitative physical model that incorporates the self-diffusion of the particles.

Trust is good, control is better: a review on monitoring and characterization techniques for flow battery electrolytes

Flow batteries (FBs) currently are one of the most promising large-scale energy storage technologies for energy grids with a large share of renewable electricity generation. Among the main technological challenges for the economic operation of a large-scale battery technology is its calendar lifetime, which ideally has to cover a few decades without significant loss of performance. This requirement can only be met if the key parameters representing the performance losses of the system are continuously monitored and optimized during the operation. Nearly all performance parameters of a FB are related to the two electrolytes as the electrochemical storage media and we therefore focus on them in this review. We first survey the literature on the available characterization methods for the key FB electrolyte parameters. Based on these, we comprehensively review the currently available approaches for assessing the most important electrolyte state variables: the state-of-charge (SOC) and the state-of-health (SOH). We furthermore discuss how monitoring and operation strategies are commonly implemented as online tools to optimize the electrolyte performance and recover lost battery capacity as well as how their automation is realized via battery management systems (BMSs). Our key findings on the current state of this research field are finally highlighted and the potential for further progress is identified.

Electrochemically Induced Changes in TiO2 and Carbon Films Studied with QCM-D

Semi-solid fluid electrode-based battery (SSFB) and supercapacitor technologies are seen as very promising candidates for grid energy storage. However, unlike for traditional batteries, their performance can quickly get compromised by the formation of a poorly conducting solid-electrolyte interphase (SEI) on the particle surfaces. In this work we examine SEI film formation in relation to typical electrochemical conditions by combining cyclic voltammetry (CV) with quartz crystal microbalance dissipation monitoring (QCM-D). Sputtered layers of typical SSFB materials like titanium dioxide (TiO₂) and carbon, immersed in alkyl carbonate solvents, are cycled to potentials of relevance to both traditional and flow systems. Mass changes due to lithium intercalation and SEI formation are distinguished by measuring the electrochemical current simultaneously with the damped mechanical oscillation. Both the TiO₂ and amorphous carbon layers show a significant irreversible mass increase on continued exposure to (even mildly) reducing electrochemical conditions. Studying the small changes within individual charge-discharge cycles, TiO₂ shows mass oscillations, indicating a partial reversibility due to lithium intercalation (not found for carbon). Viscoelastic signatures in the megahertz frequency regime confirm the formation and growth of a soft layer, again with oscillations for TiO₂ but not for carbon. All these observations are consistent with irreversible SEI formation for both materials and reversible Li intercalation for TiO₂. Our results highlight the need for careful choices of the materials chemistry and a sensitive electrochemical screening for fluid electrode systems.

Device for rheometry, impedance spectroscopy, and electrochemistry on fluid electrodes

We describe the extension of a rheometer to enable in situ impedance spectroscopy and electrochemical cycling. Key advantages of this instrument over traditional flow-channel based methods for studying fluid electrodes are the possibilities to monitor the rheological properties during cycling as well as to control the mechanical history of the sample. We describe two electrochemical configurations of the instrument, allowing fluid electrodes to be studied as full and half-cells. To demonstrate the systems' capabilities, we present characterizations of 4 different fluid electrode systems.