Revealing the Real Electrode Reaction Process of Lithium-Ion Batteries by Coupling Kinetics and Thermodynamics

Abstract

Nonuniform reactions within porous electrodes are a common phenomenon during the charge–discharge processes of lithium-ion batteries, significantly impacting their rate performance. Conventionally, researchers attribute this reaction heterogeneity to sluggish kinetics. Thermodynamics also affects the electrode process, and a sloped equilibrium potential curve can regulate the uneven electrode reaction and promote uniform lithiation of the electrode. Therefore, the real electrode process is affected by both the thermodynamics and kinetics. This work innovatively investigates the coupled effects of kinetics and thermodynamics on the electrode processes. Thermodynamic factors caused the LiNi_0.6Co_0.2Mn_0.2O₂ (NCM622) electrode to exhibit reaction rate fluctuation behavior, while the LiFePO₄ (LFP) electrode exhibited progressive reaction behavior. Then, by visualizing the electrode reaction process, the dynamic competition relationship between kinetics and thermodynamics under different working conditions was observed. The competition analysis shows that severe kinetic constraints make thermodynamic regulation ineffective, which is the main factor in the battery capacity decay. This work not only reveals the real electrode process under the coupling of kinetics and thermodynamics but also provides a more comprehensive perspective in guiding electrode design.