Lithium Concentration Dependent Elastic Properties of Battery Electrode Materials from First Principles Calculations

Abstract

This paper aims to help fill a gap in the literature on Li-ion battery electrode materials due to the absence of measured elastic constants needed for diffusion induced stress models. By examining results from new first principles density functional theory (DFT) calculations of LiCoO 2 , LiMn 2 O 4 , (and their delithiated hosts, CoO 2 and MnO 2 ), Li x Al alloys, and data from the extant literature on LiFePO 4 (and FePO 4 ), LiTi 2 O 4 (and Li 2 Ti 2 O 4 ), Li x Si, Li x Sn and lihtium graphite-interaction-compounds, a compelling picture emerges on the dependency of the elastic properties on Li concentration. Specifically, three distinct categories of behavior are found: (a) the averaged Young's moduli change very minimally upon lithiation of the spinel and olivine structures; (b) lithiation induced stiffening is observed only when new and stronger bonds between the Li ions and the host materials are formed in layered compounds; and (c) for alloy-forming electrode materials, such as Si, β-Sn and Al, the averaged Young's moduli of lithiated compounds follow the linear rule of mixtures. The tendency of ductile or brittle behavior electrode materials is investigated with the Pugh criterion, and a ductile to brittle transition was found to occur during lithiation of Al and β-Sn, but not in Si. One of the critical challenges in advanced lithium-ion (Li-ion) batteries is preventing fracture and mechanical failure of electrodes during lithium insertion and de-insertion. Most Li-ion battery electrodes experience volume changes associated with Li concentration changes within the host particles during charging and discharging.1 Graphite, for example, is the most common negative electrode for Li-ion batteries. Its volume increases by as much as 10% when Li intercalates between the sheets of C atoms.2 Compared to graphite, Si can store ∼10 times more Li, but it undergoes a massive volume expansion of the order of 300%.3 The large volume expansion, phase transition, and the associated Li diffusion-induced stresses (DIS) within electrode materials can lead to their fracture and failure which results in battery capacity loss and power fade.Significant progress toward understanding how DIS can be minimized to increase mechanical durability of Li-ion batteries 4-13 has been made. For example, Verbrugge and Cheng 11 modeled the evolution of stress and strain energy within a spherically-shaped electrode particle under either galvanostatic or potentiostatic operation. They also investigated the effects of surface energy and surface elasticity on the stress evolution in spherical electrodes.10 Wolfenstine 14 demonstrated that using Young's modulus, fracture toughness, and volume change, a critical particle size needed to lower capacity fade could be estimated with an analytical model. Recent models have been more material specific. Woodford et al. 15 further derived a failure criterion for crack propagation in individual Li x Mn 2 O 4 electrode particles during galvanostatic charging based on fracture mechanics. Using a combination...

State of Charge and State of Health Estimation Using Electrochemical Acoustic Time of Flight Analysis

“…During charge, the thickness of the cell increases: graphite expands as it lithiates, and LCO expands as it de-lithiates. 14 This acts in the opposite direction of the time of flight shift shown in Figure 4b. An increase in thickness may be anticipated to increase overall time of flight, however, the time of flight decreases during charge.…”

“…Table II shows the material properties for graphite and lithium cobalt oxide as a function of degree of lithiation. 14,19 As the cell discharges, the stiffness of the graphite decreases by a factor of >3, and the LCO stiffens by a factor of 2 (assuming full lithiation). Furthermore, the stiffness of the LCO does not change significantly until the degree of lithiation is >0.9, which occurs toward the end of discharge, depending on the lithium balance in the cell.…”

Mechanistic Analysis of Mechano-Electrochemical Interaction in Silicon Electrodes with Surface Film

“…Other mechanical properties like Poisson's ratio and fracture threshold energy also assumes different values for silicon 50 and film. 51 Correspondingly, an indicator function is used to identify the different material phases.…”

Computer Simulation of Few-Layer Graphene Intercalated by Lithium for Power Sources

“…Furthermore, one of the main problem relates to dimension instability of carbon cells caused by large possible deformation or even fracture of electrode materials due to charge -discharge processes. 1,[4][5][6][7] This paper presents results of computer simulation and density functional theory (DFT) calculations of possible configurations of nanoscaled FLG cells, containing lithium, with using local density approximation (LDA) 8,9 and one of the fastest method of energy optimization 10 within Dmol3. Furthermore, the effective way of modifying their mechanical properties with producing so called bridge-like radiation defects [11][12][13][14] is suggested.…”