Li Cathode Research Articles

A finite strain model of stress, diffusion, plastic flow, and electrochemical reactions in a lithium-ion half-cell

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 particular, we find that that stress directly influences the rest potential at the interface, so that a term involving stress must be added to the Nernst equation if the stress in the solid is significant. The model is used to predict the variation of stress and electric potential in a model 1-D half-cell, consisting of a thin film of Si on a rigid substrate, a fluid electrolyte layer, and a solid Li cathode. The predicted cycles of stress and potential are shown to be in good agreement with experimental observations.

Towards optimized preparation of cathode materials: How can modeling and concepts be used in practice

A typical state-of-the-art Li cathode is a composite material consisting of many (nano) phases so its overall kinetics can be extremely sophisticated. In this paper we first show how one can identify selected important kinetic steps that may crucially affect the overall electrode performance. Based on relatively simple concepts supported with selected model experiments, we also give several practical recipes that might be helpful for designing of cathodes with improved overall kinetics.

Measurement of concentration profile during charging of Li battery anode materials in LiClO 4-PC electrolyte

Li metal was galvanostatically electrodeposited on a horizontally positioned, downward-facing Li metal cathode in 0.5 M LiClO 4-PC electrolyte. The refractive index profile corresponding to the transient Li + ion concentration profile formed in the electrolyte solution upon applying a current step was measured in-situ by holographic interferometry. The configuration of the electrolytic cell was such that mass transfer was governed only by transient diffusion and migration, in the absence of convection. Between the moment of closing the current circuit and the time at which the interference fringes started to shift, an incubation period was observed. Such an incubation period had earlier been observed in lithium electrodeposition at a vertical planar Li metal cathode. The incubation period for the horizontal Li cathode was roughly half that for a vertical one. To study the effect of the electrode material on the incubation period, interferometry measurements were also made at an electrodeposited Ni–Sn alloy electrode. The concentration profile formed near the Ni–Sn alloy electrode during lithiation (alloying or intercalation of Li + into the electrode) agrees well with predictions made by means of the one-dimensional diffusion equation. Only very short incubation period was detected, but the magnitude was negligibly smaller than that of Li metal electrodeposition. The incubation period therefore appears to be characteristic for Li metal electrode only.

Packing, Intercalation and Compression: Determination of Operating Stresses in Composite Li Cathodes

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