Nanospinbar-Assisted Convective Ionic Transfer Toward Dendrite-Free Li Metal Batteries
Authors: Lim Minhong , Kim Suhwan , Kang Junsik , Jin Dahee , An Hyeongguk , Lee Hyuntae , Park Joonam , Lee Mingyu , Seo Jiyeon , Lee Hochun , Lee Yong Min , Lee Hongkyung 
Published: September 2023

Building high-energy-density batteries with Li-metal anodes (LMAs) featuring ultrahigh specific capacity (3860 mAh g−1) and low working voltage (−3.04 V vs. SHE) have been revisited to surpass the energy density limit of current Li-ion batteries. For instance, a successful transition from conventional graphite (372 mAh g–1) to ultrathin LMAs can deliver higher cell energies (over 500 Wh kg–1). Nonetheless, Li electrodeposition is challenging due to the dendrite formation and random growth. Extensive Li dendrite growth can enlarge the active surface area where side reactions occur, thereby severely deteriorating the Li surface and depleting the electrolyte, leading to poor cycling stability. Eventually, the Li dendrite tips can pierce the separator, causing cell short-circuiting, thereby increasing the safety risk. This is a major hurdle that must be overcome prior to commercialization. Therefore, inhibiting uneven dendritic Li plating is essential for safe and stable cycling of rechargeable lithium metal batteries (LMBs).

Inhibiting uneven, dendritic Li electroplating is crucial for the safe and stable cycling of LMBs. Homogeneous, fast Li+ transport toward the Li surface is required for uniform, dendrite-free deposition. Electrodeposition strongly depends on the mass transfer of the ionic species. In a diffusion-limited regime, such as higher currents and lack of convection, inherently limited Li+ diffusion causes a strong concentration gradient or even total Li+ depletion. Moreover, traditional ionic transport of static liquid electrolytes involving electromigration and molecular diffusion can trigger a greater disparity in Li concentration over the Li surface, leading to irregular dendrite growth.

This study presents a microturbulence-assisted convective Li+ transfer for suppressing dendrite growth using a magnetic nanospinbar (NSB)-dispersed colloidal electrolyte. We synthesized an ultrahigh-aspect-ratio NSB consisting of a paramagnetic Fe3O4 nanoparticle array and a silica outer coating. Manipulating the external electromagnetic force can remotely control the rotation of individual NSBs without dispersion failure, thereby generating a microturbulence flow inside the cell. Regardless of the electrolyte composition, rotating the NSB can reduce the Li+ diffusion layer thickness from the bulk and evenly redistribute Li+ flux over the Li surface, thereby suppressing Li dendrite growth. The NSB-dispersed electrolyte with advanced salt/solvent compositions demonstrated stable cycling of LMBs over 600 cycles at 70% capacity retention, thereby outperforming the NSB-free cell.

Figure. 1. Concept of convective Li+ transfer assisted by remote NSB stirring. Apart from stagnant electrolytes, magnetic-field-responsive NSB dispersed in the liquid electrolyte can redistribute Li+ flux near LMA through remote stirring, enabling facile, homogenous Li+ transfer and thereby leading to uniform, dendrite-free Li electroplating

Figure 1