Electrolyte-Swollen Polymer Films Enhancing Native Solid Electrolyte Interphase on Lithium Metal Anode

The lithium (Li) metal has been regarded as one of the most promising anode materials for rechargeable Li batteries thanks to its high theoretical specific capacity (3860 mAh g^-1) and low redox potential (-3.040 V vs the standard hydrogen electrode). However, the Li metal shows its inherent instability and high reactivity with electrolytes, leading to the formation of instantaneous and indiscriminating solid-electrolyte interphase (SEI) layers. The resultant fragile SEI can be broken and regenerated during repetitive discharge-charge cycles, thus provoking severe corrosion of Li metal anode, excessive electrolyte depletion and accumulation of substantial SEI layers. The inhomogeneous Li-ion migration within the irregular interphase can cause drastic growth of lithium metal dendrites and dead lithium, resulting in rapid capacity decay, poor battery lifetime, and even safety hazards. Herein, we demonstrate the electrolyte-swellable polymer thin nanolayer directly on Li metal anode by using initiated chemical vapor deposition process. The ultra-thin poly(dimethylaminomethyl styrene) (pDMAMS) layer, with a thickness of 100 nm, exhibits swelling behavior with a significant volumetric increase of 264 % under a commercial carbonate electrolyte. The corresponding expanded polymer matrix enables the formation of favorable native SEI layers within the framework, while simultaneously allowing efficient transport of Li ions. The electrolyte-swollen soft scaffold provides for Li₂O-free and Li₂CO₃-rich native SEI layers with homogeneous distribution of SEI components, achieving a remarkably high Li-ion transference number of 0.95 and ionic conductivity of 6.54 mS cm⁻¹. The pDMAMS-coated Li metal anodes prolong the battery lifetime by 550 % in Li-Li symmetric cells and 600 % in full cells coupled with practical high-nickel cathode of LiNi_0.6Mn_0.2Co_0.2O₂ in comparison to uncoated Li metal anodes. The electrolyte solvogel system is thoroughly investigated through in-depth profile analysis of SEI layers and precise manipulation of electrolyte-phobic repeating units in pDMAMS/electrolyte-phobic copolymers. This dual-purpose solvogel approach offers a fresh perspective on stabilizing the interface between the Li metal anode and the liquid electrolyte, making it widely applicable in next-generation rechargeable batteries. Furthermore, it is expected to provide impetus for advancing beyond Li-ion technologies through a novel design of SEI layers.