Modelling Coupled Transport in Solid Electrolytes
Polymer-electrolyte and solid-oxide fuel cells are on the verge of commercialisation; a gap in comprehension of the behaviour of solid electrolytes employed in these devices remains one of the key obstacles in realising their potential. Recent studies lay great emphasis on investigating the interplay between mechanical and electrochemical processes occurring in solid electrolytes, to improve the performance and lifetime of these devices, and helping them become economically feasible. With Li batteries contemplating the use of ceramic electrolytes, it becomes even more critical to understand solid electrode-solid electrolyte interfacial effects. Although the current models can describe ionic transport competently, they have not yet evolved to include mechanical effects, and electrochemical/mechanical coupling with rigour. The prime objective of this work is to develop a macroscopic model for solid electrolytes, which integrates transport, kinetic, and mechanical processes with thermodynamic consistency. The expansive literature on modelling transport in constrained polymer-electrolyte membranes will be leveraged to develop a general framework that incorporates electrochemical/mechanical coupling, and can accommodate the specificities of different physical systems.
Objective: Identifying the minimal elastic modulus of separator materials for dendrite inhibition in lithium-metal batteries.
Summary: While lithium metal polymer batteries (LMPBs) possess sufficient energy density for a competitive full-electric vehicle, they suffer from poor safety and cycle performance. The failure of LMPBs in the rechargeable applications is attributed to dendrite formation. Experiments have suggested that using additives, such as fumed slica nanoparticles, to increase the mechanical strength of the polymer domains inhibits dendrite formation. Here we develop a rigorous electrochemical model framework based on Nernst-Planck theory to study the effects of rheological and elastic properties on the kinetics of dendrite growth. A linear stability analysis is performed to identify the critical elastic modulus and transport properties of separator materials for reliable lithium-metal batteries.
A contour plot of the eigenvalues of the governing equations, with contemporary lithium battery properties.The electrode surface instability occurring in the ordinary operating regimes demonstrates the necessityof using separator materials with enhanced mechanical strength.
Convection Battery Modeling
Objective: Provide analytic and numerical approaches to a novel flow battery system.
Summary: Suppes et al have introduced novel type of flow battery, which includes porous electrodes, an electrolyte (KOH), and a mechanical pump that initiates an enhanced flow of electrolytes between electrodes. All active materials remained in a solid state in the electrodes; and the circulation of the electrolyte can be increased by the pump to enhance the mass transfer rate of the ionic intermediates. This system raises an interesting challenge for computational modelers because the transport rate is increased by convection to enhance the battery-potential. The modeling of this system will include a non-negligible convection term in the Nernst-Planck equation; therefore, the effect of the Peclet number in the electrochemical system will be evaluated.
Schematic of flow cell with packed bed electrodes
Transport and Thermodynamic Properties Characterziation for Binary Electrolytes
Summary: Electrolyte transport and thermodynamic properties are the key determinants of battery performance, particularly in high-power applications like electric and hybrid-electric vehicles. Poor transport properties limit a battery's charge and discharge rates and also lead to large concentration gradients within the electrolytes during cell operation. Large concentration gradients induce high overpotential that can cause many problems such as low charge/discharge efficiency and side reactions. Modeling electrolyte transport also requires accurate solution characterization, to ensure accurate predictions of the response to applied currents or voltages. Therefore, precise characterization for transport and thermodynamic properties are essential for battery design and optimization. My work sets out to provide techniques for accurate measurement of transport and thermodynamic properties of battery electrolytes, with the aim of facilitating the design of new and better batteries. Characterization techniques have been developed for the electrolytes involved in several systems, including alkaline, flow, lithium-ion, and magnesium-ion batteries.