Interplay of phase boundary anisotropy and electro-auto-catalytic surface reactions on the lithium intercalation dynamics in LiXFePO4 plateletlike nanoparticles

Abstract

Experiments on single crystal Li X FePO 4 (LFP) nanoparticles indicate rich nonequilibrium phase behavior, such as suppression of phase separation at high lithiation rates, striped patterns of coherent phase boundaries, nucleation by binarysolid surface wetting and intercalation waves. These observations have been successfully predicted (prior to the experiments) by 1D depthaveraged phase-field models, which neglect any subsurface phase separation. In this paper, using an electrochemo-mechanical phase-field model, we investigate the coherent non-equilibrium subsurface phase morphologies that develop in the abplane of platelet-like single-crystal platelet-like Li X FePO 4 nanoparticles. Finite element simulations are performed for 2D plane-stress conditions in the abplane, and validated by 3D simulations, showing similar results. We show that the anisotropy of the interfacial tension tensor, coupled with electroautocatalytic surface intercalation reactions, plays a crucial role in determining the subsurface phase morphology. With isotropic interfacial tension, subsurface phase separation is observed, independent of the reaction kinetics, but for strong anisotropy, phase separation is controlled by surface reactions, as assumed in 1D models. Moreover, the driven intercalation reaction suppresses phase separation during lithiation, while enhancing it during delithiation, by electro-autocatalysis, in quantitative agreement with in operando imaging experiments in * equal contributions † bazant@mit.edu single-crystalline nanoparticles, given measured reaction rate constants.arXiv:1802.05847v1 [cond-mat.mtrl-sci]

Size-dependent phase morphologies in LiFePO4 battery particles

“…First, the spinodal points for the onset of linear instability are shifted toward low state of charge, causing phase-separation to begin earlier during lithiation than during delithiation [34]. Second, the concentration-dependent driven reaction enhances phase separation during delithiation, when the reaction is autocatalytic, and suppresses phase separation during lithiation, when it is auto-inhibitory, an early prediction of the model [24,27,28,30,33] confirmed by multiple recent experiments [7,20,[34][35][36].…”

“…The depth-averaged approximation has proven reliable for LiFePO 4 due to the fact that elasticity promotes phase boundary alignment in the (010) plane [6,24], and the (010) surfaces where insertion occurs are quickly replenished with lithium [32]. A much larger interfacial width in the [010] direction was also recently shown to help validate the depth-averaged approximation [33]. Fig.…”

Lithium‐Battery Anode Gains Additional Functionality for Neuromorphic Computing through Metal–Insulator Phase Separation

“…Above a lower critical voltage bias that solves Equation , nucleation can occur at crystal defects or (perhaps more likely) at the electrode surfaces, where interfacial stability is influenced by surface wetting and driven electro‐autocatalytic reactions . These non‐equilibrium surface phenomena in turn control pattern formation within the bulk thin film, as has recently been observed by in situ, in operando X‐ray imaging of nano‐platelets of lithium iron phosphate, a phase‐separating Li‐ion battery material …”

Modeling the Metal–Insulator Phase Transition in LixCoO2 for Energy and Information Storage

“…The main goals of this paper are to i) develop an electro‐chemomechanical model that accounts for the two‐phase coexistence in the metal–insulator transition region, lattice expansions, and intercalation stresses due to lithium ion insertion, and thermodynamically consistent intercalation reaction kinetics in single crystalline LCO nanoparticles; ii) model the conductivity changes due to the metal–insulator transition in a polycrystalline nanoscale thin film used in LCO‐based memristor devices such as LISTA. Our theory is based on the phase‐field modeling technique, which has proved to be successful for other battery materials such as Li x FePO 4 , Li x TiO 2 , Li 4+ x Ti 5 O 12 , among others. We present our theoretical model and numerical results for static phase boundary orientations under equilibrium as well as nonequilibrium voltage curves for different values of applied current that predict the existence of voltage plateaus in the metal–insulator coexisting region, according to the Maxwell construction and in agreement with porous electrode experiments.…”