Past theories of electrode stability assume that the surface tension resists the amplification of surface roughness at cathodes and show that instability at lithium/liquid interfaces cannot be prevented by surface forces alone ͓Electrochim. Acta, 40, 599 ͑1995͔͒. This work treats interfacial stability in lithium/polymer systems where the electrolyte is solid. Linear elasticity theory is employed to compute the additional effect of bulk mechanical forces on electrode stability. The lithium and polymer are treated as Hookean elastic materials, characterized by their shear moduli and Poisson's ratios. Two-dimensional displacement distributions that satisfy force balances across a periodically deforming interface are derived; these allow computation of the stress and surface-tension forces. The incorporation of elastic effects into a kinetic model demonstrates regimes of electrolyte mechanical properties where amplification of surface roughness can be inhibited. For a polymer material with Poisson's ratio similar to poly͑ethylene oxide͒, interfacial roughening is mechanically suppressed when the separator shear modulus is about twice that of lithium.Dendrite formation presents a major obstacle to the development of practical lithium-electrode batteries. Active research into polymer electrolytes has persisted for nearly 30 years on the basis that these materials are found to strengthen cells mechanically and improve the cyclability of lithium electrodes. 1-4 Typical continuum-scale models of dendrite growth assume that surface tension resists the natural tendency of electrodes to roughen during deposition and do not incorporate other mechanical effects. 5,6 Recently a kinetic model that includes the effects of general stresses on current density distributions at roughening interfaces was proposed. 1 The model requires that stress distributions be obtained by solution of the steady-state equation of motion. Stress distributions are computed here by treating the electrode and separator as isotropic linear-elastic ͑Hookean solid͒ materials. Such materials are characterized by the Poisson's ratio and shear modulus, which are properties that result from straightforward rheometric experiments.In this paper, the interface between the electrode and electrolyte is subjected to an idealized two-dimensional displacement of arbitrary amplitude and frequency. A unique solution to the equation of motion is specified with additional boundary conditions required by the proposed kinetic model. In the regime of small-amplitude twodimensional perturbations to the interface, analytical solutions are obtained for displacement distributions; these results are used to compute deformation profiles on either side of the interface.Known deformation profiles allow computation of the compressive stress, deformation stress, and surface tension forces that develop at an elastic interface in response to a small-amplitude periodic disturbance. Incorporation of these forces into the kinetic model demonstrates that they contribute to changes in exchan...

Dendrite growth in a parallel-electrode lithium/polymer cell during galvanostatic charging has been modeled. The growth model is surface-energy controlled, incorporating the effect of dendrite tip curvature into its dendrite growth kinetics. Using data representative of the oxymethylene-linked poly͑ethylene oxide͒/LiTFSI system, it is shown that dendrites accelerate across cells under all conditions, and that growth is always slowed by lowering the current density. Cell shorting occurs during typical charges at current densities above 75% of the limiting current. Increased interelectrode distance slows failure, but the advantages decrease as distance lengthens. A factor of 1000 increase in surface forces delays cell failure by only 6%. While larger diffusion coefficients usually extend the time to cell failure, this trend is not consistent at high transference numbers.Lithium batteries were proposed more than 30 years ago as an ideal system for high energy-density applications. In the early 1970s, organic electrolytes were discovered to form passivating films that chemically protect pure lithium electrodes over time. 1 Although this solid-electrolyte interphase ͑SEI͒ prevents chemical reaction at a state of no current, a number of failure mechanisms have been discovered that occur during cycling of lithium rechargeable batteries. One of these mechanisms is dendritic growth, first hypothesized to occur in the lithium/polymer system in 1974. 2 Dendritic lithium deposits, sometimes called mossy lithium after being subjected to multiple charges and discharges, were first directly observed in 1980. 3 Since then, scanning electron microscopy has been used to characterize more thoroughly the appearance of lithium dendrites after cell failure. 4 While work on the lithium electrode is recent, empirical observation and theoretical analysis of dendrite growth in other electrochemical systems has been pursued for years. The most significant of these results are presented here and used to prepare a model that simulates lithium dendrite growth under galvanostatic conditions. The name dendrite derives from the treelike shape of the deposit, which can range from nearly linear and pointed ͑needle-like͒ to highly branched ͑bush-like͒. Past work has primarily considered the propagation rate and morphology of dendrites. 5 Most early experiments rely on microscopy, but qualitative pictures resulting from computer simulation have been presented in the last twenty years. Aogaki 6 simulated the electrode appearance during dendrite formation using a three-dimensional linear stability analysis. Chen and Jorné 7 used a fractal growth model to show that macroscopic shapes and branching can be mimicked by changing the dendrite resistance.Many references in the current literature show the effect of additives on dendritic deposits. Most of the work on additives tends to be simple characterization, and is relatively system-specific. The goals of these experiments include developing more inert solvent/ solute mixtures, using novel anions, and in...

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Mullins-Sekerka linear stability analysis and the Barton and Bockris dendrite-propagation model are popular methods used to describe cathodic roughening and dendritic growth. These commonly cited theories employ kinetic relationships that differ in mathematical form, but both contain the effects of surface tension and local concentration deviations induced by surface roughening. Here, a kinetic model is developed which additionally includes mechanical forces such as elasticity, viscous drag, and pressure, showing their effect on exchange current densities and potentials at roughening interfaces. The proposed expression describes the current density in terms of applied overpotential at deformed interfaces with arbitrary three-dimensional interfacial geometry. Both the Mullins-Sekerka and the Barton-Bockris kinetics can be derived as special cases of the general expression, thereby validating the proposed model and elucidating the fundamental assumptions on which the two previous theories rely.

Lithium dendrite (filament) propagation through ceramic electrolytes, leading to short-circuits at high rates of charge, is one of the greatest barriers to realising high energy density all-solidstate lithium anode batteries. Utilising in-situ X-ray computed tomography coupled with spatially mapped X-ray diffraction, the propagation of cracks and the propagation of lithium dendrites through the solid electrolyte have been tracked in a Li/Li6PS5Cl/Li cell as a function of the charge passed. On plating, cracking initiates with spallation, conical "pothole"-like cracks that form in the ceramic electrolyte near the surface with the plated electrode. The spallations form predominantly at the lithium electrode edges where local fields are high. Transverse cracks then propagate from the spallations across the electrolyte from the plated to the stripped electrode. Lithium ingress drives the propagation of the spallation and transverse cracks by widening the crack from the rear, i.e. the crack front propagates ahead of the Li. As a result, cracks traverse the entire electrolyte before the Li arrives at the other electrode and therefore before a short-circuit occurs.