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Unformatted text preview: III. Thermodynamics Lecture 10: Li-ion Batteries Notes by A. Andrew D. Jones (and MZB) In the previous section we considered the open-circuit voltage of fuel cells and primary batteries. In this section we will discuss the open-circuit voltage of secondary (rechargeable) Li-ion batteries, or “rocking chair" bat- teries, where lithium ions are shuttled between different host materials in the anode and cathode, with a preference for the latter that sets the open circuit voltage. The host compound is typically a crystalline material, such as graphite in the anode or a transition-metal oxide such as CoO 2 in the cathode, dispersed in a porous electrode as a fine powder of nanoparticles, mixed with an electron-conducting additive (e.g. carbon black) and binder material, all soaked in a liquid electrolyte. This process of intercalation of lithium in a host solid particle is reversible and does not alter its crystal structure, although there is some elastic coherency strain due to local dis- tortion of the crystal. In certain host materials, such as FePO 4 , intercalated Li ions also experience attractive forces, which can lead to the tendency for phase separation into Li-rich and Li-poor regions. Here, we will discuss very simple models for the open circuit voltage versus filling fraction, based on the concept of a regular solution of particles and holes. 1 Insertion Electrodes If enthalpic (and elastic) contributions to the free energy of intercalation are weak compared to entropic contributions, then we can model the interca- lation process as a “lattice gas” or “ideal mixture” of particles and holes from...
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This note was uploaded on 11/27/2011 for the course CHEMICAL E 20.410j taught by Professor Rogerd.kamm during the Spring '03 term at MIT.
- Spring '03