Phenomenological Model-Based Analysis of Lithium Batteries. Discharge, Charge, Relaxation Times Studies. Cycles Analysis

Abstract

The discharge and charge processes operation of lithium ion batteries is addressed. A simple phenomenological model is developed in order to predict all variables values. A set of algebraic and differential equations is derived taking into account salt and Lithium balances in electrodes, in the separator, and in particles. Balances are developed for finite volumes and appropriate average values of several variables such as concentrations, current densities, and electrochemical reaction rates are introduced. Definitions of current densities regarding volume fractions are critical issues in computations. Experimental values taken from the literature for discharge processes are predicted very accurately. Constant salt concentration in the separator can be assumed and consequently the model can be analytically solved. Charge and discharge times, initial cell capacity, lost capacity and relaxation times are estimated from simple equations. The limiting processes in cell discharge can be determined. Energy efficiency and capacity usage are quantified for cycles