Thermodynamics of Electrode Materials for Lithium-Ion Batteries

Abstract

As a high energy density storage and conversion system, lithium-ion batteries require the negative electrode material (or the anode) and the positive electrode material (or the cathode) to store and release large amounts of lithium ions during charge and discharge cycles. The lithium exchange between anode and cathode occurs owing to ion transport within the electrolyte. Such an electrode reaction involves changes in the lithium-ion composition in each electrode, which in turn induces changes in the electrode material characteristics and properties including the crystal and electronic structures, and hence the chemical potential of lithium ions. As long cycle life is also an important battery requirement, structural changes within each electrode should be as benign as possible to allow for a high lithium-ion storage capability and fast electrode kinetics. In fact, from the viewpoint of electrode material, cycle life strongly depends on the initial characteristics of the active material such as high crystallinity and low level of impurities. Cycle life also relates to the thermodynamics parameters such as the lithium stoichiometry, which relates to the state of charge (SOC) or state of discharge (SOD), the electrode potential, and the kinetics parameters including the charge and discharge current rate (or C–rate) and charge and discharge voltage limits, temperature, and pressure.

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