The galvanostatic charge and discharge of a lithium anode/solid polymer separator/insertion cathode cell is modeled using concentrated solution theory. The model is general enough to include a wide range of polymeric separator materials, lithium salts, and composite insertion cathodes. Insertion of lithium into the active cathode material is simulated using superposition, thus greatly simplifying the numerical calculations. Variable physical properties are permitted in the model. The results of a simulation of the charge/discharge behavior of the LiIPEOs-LiCF~SO31TiS2 system are presented. Criteria are established to assess the importance of diffusion in the solid matrix and transport in the electrolyte. Consideration is also given to various procedures for optimization of the utilization of active cathode material.

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...

The galvanostatic charge and discharge of a dual lithium ion insertion (rocking-chair) cell are modeled. Transport in the electrolyte is described with concentrated solution theory. Insertion of lithium into and out of the active electrode material is simulated using superposition, greatly simplifying the numerical calculations. Simulation results are presented for the Li=C~lpropylene carbonate +IM LiC1OJLiyMn204 cell, and these results are compared with experimental data from the literature. Criteria are established to assess the importance of diffusion in the solid matrix and of transport in the electrolytic solution. Various procedures to optimize the utilization of active material are considered. Simulation results for the dual lithium ion insertion cell are compared with those for a cell with a solid lithium negative electrode.The storage and conversion of energy continues to be important to society. Batteries, which interconvert chemical and electrical energy, are widely used in industry and for consumer applications (e.g., appliances and laptop computers). At the same time, environmental concerns are reshaping many industries. The ecological hazards of batteries through their operation and disposal is a primary consideration for battery manufacturers. In addition, stricter emission standards on automobiles are spurring interest in batteries for electric-vehicle applications. The energy and power requirements for vehicle propulsion are rigorous. 1 Consequently, research on rechargeable battery systems is receiving renewed attention.Lithium batteries are attractive for energy storage because of their high theoretical energy densities. Furthermore, they are less toxic than nickel cadmium or lead acid cells, and their disposal poses fewer environmental problems. Although primary lithium batteries have been massproduced for years, 2 the secondary (rechargeable) lithium cell has been commercialized only recently. 3-~ The typical lithium cell is made up of a lithium metal negative electrode, an electrolyte which serves as an ionic path between electrodes and separates the two materials, and a positive electrode, such as Mn204.In general, a highly reactive material is desired for the negative electrode to give a higher cell potential, and hence a higher theoretical energy density. Unfortunately, the more reactive the electrode material the more likely it reacts irreversibly with the electrolyte. The high reactivity of lithium metal is a significant problem for lithium batteries. Successful lithium battery systems operate due to a protective film that forms on the electrode surface. ~ This protective film retards further reaction with the electrolyte but impacts the capacity and cycle life of the cell through increased resistance and material isolation. The highly reactive lithium metal is a safety issue as well, becoming especially important in larger cells.One alternative scheme has been to replace the lithium metal negative electrode with a lithium alloy or compound, such as: LiA1, 7 LiFe203, s LiW02, 8...

Modeling results for a lithium‐ion battery based on the couple LixC6|LiyMn2O4 are presented and compared to experimental data. Good agreement between simulation and experiment exists for several different experimental cell configurations on both charge and discharge. Simulations indicate that the battery in its present design is ohmically limited. Additional internal resistance in the cells, beyond that initially predicted by the model, could be described using either a contact resistance between cell layers or a film resistance on the negative electrode particles. Modest diffusion limitations in the carbon electrode arising at moderate discharge rates are used to fit the diffusion coefficient of lithium in the carbon electrode, giving Dnormals=3.9×10−10 cm2/normals . Cells with a 1 M (mol/dm3) LiPF6 initial salt concentration become solution‐phase diffusion limited at high rates. The low‐rate specific energy calculated for the experimental cells ranges from 70 to 90 Wh/kg, with this mass based on the composite electrodes, electrolyte, separator, and current collectors. The peak specific power for a 30 s current pulse to a 2.8 V cutoff potential is predicted to fall from about 360 W/kg at the beginning of discharge to 100 W/kg at 80% depth of discharge for one particular experimental cell. Different system designs are explored using the mathematical model with the objective of a higher specific energy. Configurations optimized for a 6 h discharge time should obtain over 100 Wh/kg.