No 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.

Inhibiting uneven dendritic Li electroplating is crucial for the safe and stable cycling of Li metal batteries (LMBs). Homogeneous and fast Li+ transport towards the Li surface is required for uniform and dendrite‐free deposition. However, the traditional ionic transport of static liquid electrolytes involving electromigration and molecular diffusion can trigger a greater disparity in the Li concentration over the Li surface, leading to irregular dendrite growth. Here, a convective Li+ transfer for suppressing dendrite growth through magnetic nanospinbar (NSB)‐dispersed colloidal electrolytes is presented. An ultrahigh‐aspect‐ratio NSB consisting of a paramagnetic Fe3O4 nanoparticle array and silica outer coating is synthesized. Manipulating the external electromagnetic force can remotely control the rotation of individual NSBs without dispersion failure, thereby generating mesoscale turbulence inside the cells. Regardless of the electrolyte composition, rotating the NSB can reduce the Li+ diffusion layer thickness from the bulk and evenly redistribute the Li+ flux over the Li surface, thereby suppressing Li dendrite growth. The NSB‐dispersed electrolyte with advanced salt/solvent compositions demonstrates stable cycling of LMBs over 600 cycles with 70% capacity retention, thereby outperforming the NSB‐free cell.

Dynamic Ionic Transport In article number 2204052, Hochun Lee, Yong Min Lee, Hongkyung Lee, and co‐workers demonstrate Li dendrite suppression with 1‐μm long, magnetic nanospinbar (NSB) dispersed electrolytes. Spatially distributed NSBs within various electrolytes can generate mesoscale turbulence actuated by an external rotating magnetic field. NSB‐assisted dynamic Li+ transfer enables fast and uniform seeding of Li nuclei, inhibiting dendritic Li electroplating, thereby leading to stable cycling of Li‐metal batteries. Dynamic ionic transfer via NSB colloids opens new possibilities for out of mass‐transfer‐limit in various electrochemical systems.