Analysis of Lithium-Ion Cell Deterioration through Parameter Measurement

Abstract

Deterioration analysis of aged lithium-ion cells is becoming increasingly important as demand for longer life of cells increases for electric vehicles and energy storage systems. In this work, we propose a non-destructive analysis of the degree of deterioration of aged cells by measuring the physicochemical parameters. Low-rate charge-discharge, galvanostatic intermittent titration technique, and electrochemical impedance spectroscopy were used to measure the quasi-equilibrium potential, diffusion coefficient, and exchange current density of the active material in graphite / NCM cell after cycling aging. Loss of active material, loss of lithium inventory, and the internal resistance changes of aged cell were analyzed from differential voltage analysis and capacity variations after aging. Then the measured kinetics and mass transfer related parameters were compared with those of fresh active materials and analyzed as functions of aging conditions. The changes of quasi-equilibrium potential is attributed to the loss of active materials, and decreased kinetic parameters and increased resistances show the formation of inactive phases or byproducts that cause pore structure changes of electrodes.