Aashutosh Mistry

State-of-the-art and Future Research Needs for Multiscale Analysis of Li-ion Cells

Author(s): Shah, K; Balsara, N; Banerjee, S; Chintapalli, M; Cocco, AP; Chiu, WKS; Lahiri, I; Martha, S; Mistry, A; Mukherjee, PP; Ramadesigan, V; Sharma, CS; Subramanian, VR; Mitra, S; Jain, A | Abstract: The performance, safety, and reliability of Li-ion batteries are determined by a complex set of multiphysics, multiscale phenomena that must be holistically studied and optimized. This paper provides a summary of the state of the art in a variety of research fields related to Li-ion battery materials, processes, and systems. The material presented here is based on a series of discussions at a recently concluded bilateral workshop in which researchers and students from India and the U.S. participated. It is expected that this summary will help understand the complex nature of Li-ion batteries and help highlight the critical directions for future research.

Secondary-Phase Stochastics in Lithium-Ion Battery Electrodes

Lithium-ion battery electrodes exhibit complex interplay among multiple electrochemically coupled transport processes, which rely on the underlying functionality and relative arrangement of different constituent phases. The electrochemically inactive solid phases (e.g., conductive additive and binder, referred to as the secondary phase), while beneficial for improved electronic conductivity and mechanical integrity, may partially block the electrochemically active sites and introduce additional transport resistances in the pore (electrolyte) phase. In this work, the role of mesoscale interactions and inherent stochasticity in porous electrodes is elucidated in the context of short-range (interface) and long-range (transport) characteristics. The electrode microstructure significantly affects kinetically and transport-limiting scenarios and thereby the cell performance. The secondary-phase morphology is also found to strongly influence the microstructure-transport-kinetics interactions. Apropos, strategies have been proposed for performance improvement via electrode microstructural modifications.

Mesoscale Physicochemical Interactions in Lithium–Sulfur Batteries: Progress and Perspective

The shuttle effect and poor conductivity of the discharge products are among the primary impediments and scientific challenges for lithium–sulfur batteries. The lithium–sulfur battery is a complex energy storage system, which involves multistep electrochemical reactions, insoluble polysulfide precipitation in the cathode, soluble polysulfide transport, and self-discharge caused by chemical reactions between polysulfides and Li metal anode. These phenomena happen at different length and time-scales and are difficult to be entirely gauged by experimental techniques. In this paper, we reviewed the multiscale modeling studies on lithium–sulfur batteries: (1) the atomistic simulations were employed to seek alternative materials for mitigating the shuttle effect; (2) the growth kinetics of Li2S film and corresponding surface passivation were investigated by the interfacial model based on findings from atomistic simulations; (3) the nature of Li2S2, which is the only solid intermediate product, was revealed by the density functional theory simulation; and (4) macroscale models were developed to analyze the effect of reaction kinetics, sulfur loading, and transport properties on the cell performance. The challenge for the multiscale modeling approach is translating the microscopic information from atomistic simulations and interfacial model into the meso-/macroscale model for accurately predicting the cell performance. [DOI: 10.1115/1.4037785]

Electrochemistry Coupled Mesoscale Complexations in Electrodes Lead to Thermo-Electrochemical Extremes

Thermo-electrochemical extremes continue to remain a challenge for lithium-ion batteries. Contrary to the conventional approach, we propose herein that the electrochemistry-coupled and microstructure-mediated cross talk between the positive and negative electrodes ultimately dictates the off-equilibrium-coupled processes, such as heat generation and the propensity for lithium plating. The active particle morphological differences between the electrode couple foster a thermo-electrochemical hysteresis, where the difference in heat generation rates changes the electrochemical response. The intrinsic asymmetry in electrode microstructural complexations leads to thermo-electrochemical consequences, such as cathode-dependent thermal excursion and co-dependent lithium plating otherwise believed to be anode-dependent.

Axisymmetric model of drop spreading on a horizontal surface

Spreading of an initially spherical liquid drop over a textured surface is analyzed by solving an integral form of the governing equations. The mathematical model extends Navier-Stokes equations by including surface tension at the gas-liquid boundary and a force distribution at the three phase contact line. While interfacial tension scales with drop curvature, the motion of the contact line depends on the departure of instantaneous contact angle from its equilibrium value. The numerical solution is obtained by discretizing the spreading drop into disk elements. The Bond number range considered is 0.01–1. Results obtained for sessile drops are in conformity with limiting cases reported in the literature [J. C. Bird et al., “Short-time dynamics of partial wetting,” Phys. Rev. Lett. 100, 234501 (2008)]. They further reveal multiple time scales that are reported in experiments [K. G. Winkels et al., “Initial spreading of low-viscosity drops on partially wetting surfaces,” Phys. Rev. E 85, 055301 (2012) and A. Eddi et al., “Short time dynamics of viscous drop spreading,” Phys. Fluids 25, 013102 (2013)]. Spreading of water and glycerin drops over fully and partially wetting surfaces is studied in terms of excess pressure, wall shear stress, and the dimensions of the footprint. Contact line motion is seen to be correctly captured in the simulations. Water drops show oscillations during spreading while glycerin spreads uniformly over the surface.

Spreading of a pendant liquid drop underneath a textured substrate

A pendant drop spreading underneath a partially wetting surface from an initial shape to its final equilibrium configuration and contact angle is studied. A mathematical formulation that quantifies spreading behavior of liquid drops over textured surfaces is discussed. The drop volume and the equilibrium contact angle are treated as parameters in the study. The unbalanced force at the three-phase contact line is modeled as being proportional to the degree of departure from the equilibrium state. Model predictions are verified against the available experimental data in the literature. Results show that the flow dynamics is strongly influenced by the fluid properties, drop volume, and contact angle of the liquid with the partially wetting surface. The drop exhibits rich dynamical behavior including inertial oscillations and gravitational instability, given that gravity tries to detach the drop against wetting contributions. Flow characteristics of drop motion, namely, the radius of the footprint, slip lengt...

Probing spatial coupling of resistive modes in porous intercalation electrodes through impedance spectroscopy

In porous intercalation electrodes, coupled charge and species transport interactions take place at the pore-scale, while often observations are made at the electrode-scale. The physical manifestation of these interactions from pore- to electrode-scale is poorly understood. Moreover, the spatial arrangement of the constituent material phases forming a porous electrode significantly affects the multi-modal electrochemical and transport interplay. In this study, the relation between the electrode specification, resultant porous microstructure, and electrode-scale resistances is delineated based on a virtual deconvolution of the impedance response. Relevant short- and long-range interactions are identified. Without altering the microstructural arrangement, if the electrode thickness is increased, the resistances do not scale linearly with thickness. This dependence is also probed to identify the fundamental origins of thick electrode limitations.

Multiscale model reduction for pore-scale simulation of Li-ion batteries using GMsFEM

Abstract In this work, we consider electrochemical processes for the pore-scale simulation of Lithium-ion batteries (LIBs). Mathematical model consists of the coupled system of the equations for the concentration and electric potential. We develop fine-scale approximation using discontinuous Galerkin approach, where interface condition is imposed weakly. We present novel multiscale model reduction technique based on the GMsFEM, where multiscale basis functions are constructed using information about variation of the medium at the micro level. We present numerical results for two cases of the boundary conditions and compare errors for different coarse grids for testing the proposed computational multiscale method. Numerical results show that the multiscale basis functions can efficiently capture the information of the fine-scale features of the medium with significant dimension reduction of the system and provide accurate solutions.