Physicochemical nature of polarization components limiting the fast operation of Li-ion batteries

Abstract

High-power Li-ion batteries (LIBs) are widely used in electric vehicles and grid storage applications and are therefore in high demand; however, their realization requires a fundamental understanding of electrochemical polarization arising during charge/discharge reactions. To date, electrochemical polarization is poorly understood because of the complexity of experimental measurements and the lack of a proper theory of the microscopic structure of the electrolyte solution and complicated interactions among solution species. The present work comprehensively reviews the components of this polarization and discusses their physicochemical nature, focusing on those due to (i) Ohmic polarization in the electrolyte, (ii) interfacial charge transfer, (iii) concentration gradients in solid and electrolyte phases, (iv) ion transport within the electrode pores, and (v) the electronic resistance of the composite electrode and current collector interface. We also briefly touch on today's understanding of the microscopic structure of LIB electrolytes and the experimental analysis of polarization sources, subsequently addressing the relative contributions of polarization components and their dependence on diverse parameters, for example, electrode/electrolyte materials and the dimensional factors of composite electrodes (thickness/porosity/tortuosity). Thus, this review is expected to assist the setting of correct battery R&D targets and aid the identification of delusive studies that lack a comprehensive understanding of the physicochemical nature of electrochemical polarization and therefore report unrealistic high-power performances.