Lithium intercalation into graphite is the foundation for the lithium-ion battery, and the thermodynamics of the lithiation of graphitic electrodes have been heavily investigated. Intercalated lithium in bulk graphite undergoes structural ordering known as staging to minimize electrostatic repulsions within the crystal lattice. While this process is well-understood for bulk graphite, confinement effects become important at the nanoscale, which can significantly impact the electrochemistry of nanostructured electrodes. Therefore, graphene offers a model platform to study intercalation dynamics at the nanoscale by combining on-chip device fabrication and electrochemical intercalation with in situ characterization. We show that microscale mechanical strain significantly affects the formation of ordered lithium phases in graphene. In situ Raman spectroscopy of graphene microflakes mechanically constrained at the edge during lithium intercalation reveals a thickness-dependent increase of up to 1.26 V in the electrochemical potential that induces lithium staging. While the induced mechanical strain energy increases with graphene thickness to the fourth power, its magnitude is small compared to the observed increase in electrochemical energy. We hypothesize that the mechanical strain energy increases a nucleation barrier for lithium staging, greatly delaying the formation of ordered lithium phases. Our results indicate that electrode assembly can critically impact lithium staging dynamics important for cycling rates and power generation for batteries. We demonstrate strain engineering in two-dimensional nanomaterials as an approach to manipulate phase transitions and chemical reactivity.
The possibility of tuning the vibrational properties and the thermal conductivity of layered van der Waals materials either chemically or mechanically paves the way to significant advances in nanoscale heat management. Using first-principles calculations we investigate the modulation of heat transport in MoS2 by lithium intercalation and cross-plane strain. We find that both the in-plane and cross-plane thermal conductivity (kr, kz) of MoS2 are extremely sensitive to both strain and electrochemical intercalation. Combining lithium intercalation and strain, the in-plane and cross-plane thermal …
Room-temperature (RT) conductivity of most candidates for solid electrolytes of miniaturized lithium-ion batteries is still 1-2 orders of magnitude below commercial requirements, therefore several approaches are being pursued aiming the enhancement of such values. In this letter, we report for the first time direct theoretical evidence that epitaxial strain can be an efficient tool to reach this goal.
(Li,Al)-co-doped magnesium spinel (Li$_x$Mg$_{1-2x}$Al$_{2+x}$O$_4$) is a solid lithium-ion electrolyte with potential use in all-solid-state lithium-ion batteries. Interfaces with spinel electrodes, such as Li$_y$Mn$_2$O$_4$ and Li$_{4+3z}$Ti$_5$O$_{12}$, may be lattice-matched, with potentially low interfacial resistances. Small lattice parameter differences across a lattice-matched interface are unavoidable, causing residual epitaxial strain. This strain potentially modifies lithium diffusion near the interface, contributing to interfacial resistance. Here we report a density functional the…
In this letter, we study the stability of the domain model for lithium intercalated graphite in stages III and II by means of Density Functional Theory and Kinetic Lattice Monte Carlo simulations. We find that the domain model is either thermodynamically or kinetically stable when compared to the standard model in stages III and II. The existence of domains in the intercalation sequence is well supported by recent high resolution transmission electron microscope observations in lithiated graphite. Moreover, we predict that such domain staging sequences leads to a wide range of diffusivity as r…
Lithium ion batteries (LIBs) work under sophisticated external force field and its electrochemical properties could be modulated by strain. Owing to the electro-mechanical coupling, the change of micro-local-structures can greatly affect lithium (Li) diffusion rate in solid state electrolytes and electrode materials of LIBs. In this study, we find that strain gradient in bilayer graphene (BLG) significantly affects Li diffusion barrier, which is termed as the flexo-diffusion effect, through first-principles calculations. The Li diffusion barrier substantially decreases/increases under the posi…
The influence of elastic strain on the lithium vacancy formation and migration in bulk LiCoO2 is evaluated by means of first-principles calculations within density functional theory (DFT). Strain dependent energies are determined directly from defective cells and also within linear elasticity theory from the elastic dipole tensor (Gij) for ground state and saddle point configurations. We analyze finite size-effects in the calculation of Gij, compare the predictions of the linear elastic model with those obtained from direct calculations of defective cells under strain and discuss the differenc…
Strain effects on the stability, electronic structure, and hydrogen storage capacity of lithium-doped graphane (CHLi) have been investigated by stateof-the art first principle density functional theory (DFT). Molecular dynamics MD) simulations have confirmed the stability of Li on graphane sheet when it is subject to 10% of tensile strain. Under biaxial asymmetric strain, the binding energy of Li of graphane (CH) sheet increases by 52% with respect to its bulk's cohesive energy. With 25% doping concentration of Li on CH sheet,the gravimetric density of hydrogen storage is found to reach up to …
A phenomenological treatment of domain walls based on the Ginzburg-Landau-Devonshire theory is developed for uniaxial, trigonal ferroelectrics lithium niobate and lithium tantalate. The contributions to the domain wall energy from polarization and strain as a function of orientation are considered. Analytical expressions are developed which are analyzed numerically to determine the minimum polarization, strain, and energy configurations of domain walls. It is found that hexagonal y-walls are preferred over x-walls in both materials. This agrees well with experimental observation of domain geom…
We present a new way to enhance the electron-phonon coupling constant and the critical superconducting temperature of graphene, significantly beyond all reported values. Using density functional theory, we explore the application effects of the tensile biaxial strain on the lithium intercalated graphene. Both effects together, the presence of adatom and the strain, trigger enhancement of critical temperature, up to 300\%, compared to non-strained lithium intercalated graphene.
Dendrite formation is a major obstacle, such as capacity loss and short circuit, to the next-generation high-energy-density lithium (Li) metal batteries. The development of successful Li dendrite mitigation strategies is impeded by an insufficient understanding of Li dendrite growth mechanisms. Li-plating-induced internal stress in Li metal and its effect on dendrite growth have been studied in previous models and experiments, while the underlying microcosmic mechanism is elusive. Here, we analyze the role of plating-induced stress in dendrite formation through first-principles calculations an…
Can Strain or Anion Interchange Make an Unstable Structure Stable? Energetics, Lattice Dynamics and Strain-Tunable Band Gaps of Lithium Chalcohalide Antiperovskites (Li$_{3}$$BA$) and their Anion Interchange Variants (Li$_{3}$$AB$)
Structural strain severely impacts material properties such as the linear and non-linear optical response. Moreover, strain plays a key role, e.g., in the physics of ferroelectrics and in particular of their domain walls. $μ$-Raman spectroscopy is a well-suited technique for the investigation of such strain effects, as it allows to measure the lattice dynamics locally. However, quantifying and reconstructing strain fields from Raman maps requires knowledge on the strain dependence of phonon frequencies. In this work, we have analyzed both theoretically and experimentally the phonon frequencies…
We formulate the continuum field equations and constitutive equations that govern deformation, stress, and electric current flow in a Li-ion half-cell. The model considers mass transport through the system, deformation and stress in the anode and cathode, electrostatic fields, as well as the electrochemical reactions at the electrode/electrolyte interfaces. It extends existing analyses by accounting for the effects of finite strains and plastic flow in the electrodes, and by exploring in detail the role of stress in the electrochemical reactions at the electrode-electrolyte interfaces. In part…
Real-time stress evolution in a graphite-based lithium-ion battery negative-electrode during electrolyte wetting and electrochemical cycling is measured through wafer-curvature method. Upon electrolyte addition, the composite electrode rapidly develops compressive stress of the order of 1-2 MPa due to binder swelling; upon continued exposure, the stress continues to evolve towards an apparent plateau. During electrochemical intercalation at a slow rate, the compressive stress increases with the electrode's state-of-charge, reaching a maximum value of 10 - 12 MPa. There appears to be an approxi…
Lithium-intercalated layered transition-metal oxides, LixTMO2, brought about a paradigm change in rechargeable batteries in recent decades and show promise for use in memristors, a type of device for future neural computing and on-chip storage. Thermal transport properties, although being a crucial element in limiting the charging/discharging rate, package density, energy efficiency, and safety of batteries as well as the controllability and energy consumption of memristors, are poorly managed or even understood yet. Here, for the first time, we employ quantum calculations including high-order…
We systematically investigate the effect of strain and doping on the polar metal phase in lithium osmate, LiOsO$_3$, using first-principles calculations. We demonstrate that the polar metal phase in LiOsO$_3$ can be controlled by biaxial strain. Based on density functional calculations, we show that a compressive biaxial strain enhances the stability of the polar $R3c$ phase. On the other hand, a tensile biaxial strain favors the centrosymmetric $R\overline{3}c$ structure. Thus, strain emerges as a promising control parameter over polar metallicity in this material. We uncover a strain-driven …
Beyond Lithium-Ion Batteries: Are Effective Electrodes Possible for Alkaline and Other Alkali Elements? Exploring Ion Intercalation in Surface-Modified Few-Layer Graphene and Examining Layer Quantity and Stages
It is of critical importance to understand the mechanical properties change of electrode materials during lithium intercalation in the mechanical design of Li-ion batteries, for the purpose of the high reliability and safety in their applications. Here, we investigated the mechanical properties of both bulk and single layer phosphorus during the lithium intercalation process by using the first-principles calculations. Our results show that the Young's modulus of bulk and layered phosphorus strongly depends on the lithium intercalation. The mechanical bearing capacities, such as critical strain…
We present detailed multi frequency resonant Raman measurements of potassium graphite intercalation compounds (GICs). From a well controlled and consecutive in-situ intercalation and high temperature de-intercalation approach the response of each stage up to stage VI is identified. The positions of the G and 2D lines as a function of staging depend on the charge transfer from K to the graphite layers and on the lattice expansion. Ab-initio calculations of the density and the electronic band-structure demonstrate that most (but not all) of the transferred charge remains on the graphene sheets a…
The existence of passivating layers at the interfaces is a major factor enabling modern lithium-ion (Li-ion) batteries. Their properties determine the cycle life, performance, and safety of batteries. A special case is the solid electrolyte interphase (SEI), a heterogeneous multi-component film formed due to the instability and subsequent decomposition of the electrolyte at the surface of the anode. The SEI acts as a passivating layer that hinders further electrolyte disintegration, which is detrimental to the Coulombic efficiency. In this work, we use first-principles simulations to investiga…
To study the electrochemical reaction on surfaces, phase interfaces, and crack surfaces in the lithium ion battery electrode particles, a phase-field model is developed, which describes fracture in large strains and anisotropic Cahn-Hilliard-Reaction. Thereby the concentration-dependency of the elastic properties and the anisotropy of diffusivity are also considered. The implementation in 3D is carried out by isogeometric finite element methods in order to treat the high order terms in a straightforward sense. The electrochemical reaction is modeled through a modified Butler-Volmer equation to…
Lithium-ion batteries exhibit complex nonlinear dynamics, resulting from diffusion and phase transformations coupled to ion intercalation reactions. Using the recently developed Cahn-Hilliard reaction (CHR) theory, we investigate a simple mathematical model of ion intercalation in a spherical solid nanoparticle, which predicts transitions from solid-solution radial diffusion to two-phase shrinking-core dynamics. This general approach extends previous Li-ion battery models, which either neglect phase separation or postulate a spherical shrinking-core phase boundary, by predicting phase separati…
A combination of experimental measurements and numerical simulations are used to characterize the mechanical and electrochemical response of thin film amorphous Si electrodes during cyclic lithiation. Parameters extracted from the experiment include the variation of elastic modulus and the flow stress as functions of Li concentration; the strain rate sensitivity; the diffusion coefficient for Li transport in the electrode; the free energy of mixing as a function of Li concentration in the electrode; the exchange current density for the Lithium insertion reaction; as well as reaction rates and …
Conversion reaction is one of the most important chemical processes in energy storage such as lithium ion batteries. While it is generally assumed that the conversion reaction is initiated by ion intercalation into the electrode material, solid evidence of intercalation and the subsequent transition mechanism to conversion remain elusive. Here, using well-defined WO3 single crystalline thin films grown on Nb doped SrTiO3(001) as a model electrode, we elucidate the conversion reaction mechanisms during Li+, Na+ and Ca2+ insertion into WO3 by in situ transmission electron microscopy studies. Int…
