The properties of rechargeable lithium ion batteries are determined by the electrochemical and kinetic properties of their constituent materials as well as by their underlying microstructure. Through this project, methods are developed that use microscopic information and constitutive material properties to calculate the response of rechargeable batteries. The methods are implemented in OOF, a public domain finite element code, so they can be applied to arbitrary two dimensional microstructures with crystallographic anisotropy. This methodology is being used as a design tool for creating improved electrode microstructures. Novel geometrical arrangements of electrode particles are explored to improve active materials utilization, power density, and reliability (electrochemical and electrical) of the LiyC | LixMn2O4, and the LiyC | LixCoO2 battery system. Analyses suggest battery performance can be improved by controlling the transport paths to the back of the cathode, maximizing the surface area for intercalating lithium ions, and carefully controlling the spatial distribution and particle size of active material (see Figure 1).
Self-organized three-dimensional rechargeable lithium-ion batteries are power sources whose individual components are brought together through colloidal self-stabilizing forces. The resulting structures are highly percolating electrode particle distributions with very short diffusion distances. These devices have the potential of outperforming classic rocking chair battery designs by decreasing the ohmic losses and localized joule heating, while simultaneously delivering higher power densities and specific energies closer to the theoretical ideal, compared to those currently provided by available technologies. In the present project, the rocking chair lithium-ion battery architecture is taken as a point of reference to explore never assembled new variations of a self-organized three-dimensional battery concept. Highly branched tortuous electrode particle distributions, perfectly ordered branches of electrode materials, and positive electrode structures with two or more chemistries are some of the approaches that are being pursued. Simulations show that the power density of a rechargeable battery can be engineered by maximizing the electrochemical driving forces for intercalation, while decreasing the characteristic transport distances of the material components. Additionally, the analyzed 3D devices greatly diminish the possibility of salt precipitation during discharge, for the microstructure limitations that exist in the classic design have been removed.
Figure 1. Voltage evolution of a typical rocking chair cathode for 1C discharge rate. Left inset shows cathode microstructure. Top row shows the color key for the voltage distribution. Bottom row illustrates color key for normalized lithium concentration distribution. Right inset shows lithium concentration at the end of discharge process. The battery is discharged when the surface of the particles is saturated with lithium ions. Note more lithium can still be accommodated within each particle.
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Voltage distribution inside microstructurally complex battery design at time intervals of 200s. Upper left inset shows modeled device. Lower left shows color key to instantaneous voltage distribution. For the present device, as the discharge of the device proceeds, transport limitations triggered by the tortuosity of the interpenetrated structure induces voltage drops.
Rechargeable Lithium-Ion Batteries
Rocking-Chair Batteries
Three-Dimensional, Self-Organized Batteries
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