Self-discharge tests to measure side-reaction currents of a Li[Li1/3Ti5/3]O4 electrode

Abstract

The lifetime performance of lithium-ion batteries is a critical issue for automobile and stationary applications. The difference in the side-reaction current (ISR) of electrodes causes deviations of the state of charge (SOC) of the electrodes leading to the capacity fading of lithium-ion batteries. Establishment of a method to measure the ISR is important for understanding the capacity fading mechanism. We report herein that a novel and simple method to determine the ISR in lithium-ion batteries, the self-discharge test, was developed and applied to lithium-ion cells with lithium titanium oxide (Li[Li1/3Ti5/3]O4, LTO), lithium aluminum manganese oxide (Li[Li0.1Al0.1Mn1.8]O4, LAMO), and lithium nickel manganese oxide (Li[Ni1/2Mn3/2]O4, LiNiMO) as electrodes. According to the self-discharge test results, the ISR of LTO is affected by another electrode of LAMO or LiNiMO. The ISR of LTO in LTO/LiNiMO cells larger than that in LTO/LAMO cells is explained by the additional-ISR of LTO, which results from side reactions such as the reduction of oxidized products generated at the positive electrode. The side reactions at the positive electrode are accelerated with increasing electrode potential, meaning that the higher potential of the positive electrode resulted in the larger additional-ISR of LTO. The real side-reaction current of the LTO electrode in lithium-ion cells is the sum of the intrinsic and the additional current (real-ISR = intrinsic-ISR + additional-ISR).