Metal Coated Polypropylene Separator with Enhanced Surface Wettability for High Capacity Lithium Metal Batteries

Abstract

Lithium metal batteries are among the strong contenders to meet the increasing energy demands of the modern world. Metallic lithium (Li) is light in weight, possesses very low standard negative electrochemical potential and offers an enhanced theoretical capacity (3860 mA h g−1). As a negative electrode Li paves way to explore variety of elements including oxygen, sulfur and various other complex oxides as potential positive electrodes with a promise of much higher energy densities than that of conventional positive electrodes. However, there are technical challenges in utilizing metallic lithium due to its higher reactivity towards liquid electrolytes and higher affinity to form Li dendrites, leading to serious safety concerns. Here, we report on preparation of niobium (Nb) metal-coated binder-free and highly hydrophilic polypropylene separator prepared via radio frequency (RF) magnetron sputtering. Thin layer of niobium metal (Nb) particles were deposited onto the polypropylene (PP) sheet for various time periods to achieve desired coating thickness. The as-prepared separator revealed excellent hydrophilic behaviour due to enhanced surface wettability. Symmetric cells display reduced interface resistance and uniform voltage profiles for 1000 cycles with reduced polarization at higher current densities suggesting smooth stripping and plating of Li and homogeneous current distribution at electrode/electrolyte interface under room temperature conditions. Nb nanolayer protected separator with LiNi0.33M0.33Co0.33O2 (LNMC) and composite sulfur cathodes revealed an enhanced cycling stability.

Uniform Lithium Deposition Achieved by SnO2/Hydroxypropyl Methyl Cellulose Composite Separator toward Ultrastable Lithium Metal Batteries

“…For this reason, modified separators with high mechanical strength, ionic conductivity, and lithophilicity are particularly significant to suppress Li dendrites. Recently, many metals that can reduce the overpotential of Li deposition such as Zn, Nb, Bi, and Ge, etc., have been used to modify separators to manage the Li + flux and inhibit the formation of Li dendrites. However, the preparation of these metal-coatings usually requires techniques including magnetron sputtering, thermal evaporation, and so on, which call for relatively complex equipment.…”

Function-directed design of battery separators based on microporous polyolefin membranes

“…135,136 The magnetron sputtering method has been used to prepare high-quality functional separators for Li metal batteries. 137–141 For example, Zhang et al reported the use of an ultrathin Cu film-coated PE separator to suppress Li dendrite growth in Li metal batteries. 140 The Cu film-coated PE separator was prepared by direct current magnetron sputtering.…”

“…Subsequently, functional separators with lithiophilic nucleation sites and lithiophilic polymers have been developed to control the dendrite growth direction, enabling the stable cycling of Li metal anodes. 130,138,141,149…”

Synergistic Composite Coating for Separators in Lithium Metal Batteries

“…24 Accordingly, separator wetting clearly needs to be improved, yet little work has been devoted to this property in the context of LMBs. 25,26 The separators in LIBs have been developed by adopting polyolefin-based porous membranes such as those manufactured from polyethylene (PE) and polypropylene (PP), as they allow Li ions to efficiently transfer through the electrolyte to fill their pores while being viable for large-scale manufacturing at a low cost. 27 Their intrinsic shortcomings of poor thermal stability and mechanical strength, which cause internal short circuits and ultimately a fire hazard, have been mainly addressed by coating them with ceramic particles.…”

“…Although ILs are safe to use and offer good stability in contact with metallic Li, their direct incorporation into practical cells is problematic because their poor wettability with the separator and high viscosity both adversely affect charge transport kinetics . Accordingly, separator wetting clearly needs to be improved, yet little work has been devoted to this property in the context of LMBs. , The separators in LIBs have been developed by adopting polyolefin-based porous membranes such as those manufactured from polyethylene (PE) and polypropylene (PP), as they allow Li ions to efficiently transfer through the electrolyte to fill their pores while being viable for large-scale manufacturing at a low cost . Their intrinsic shortcomings of poor thermal stability and mechanical strength, which cause internal short circuits and ultimately a fire hazard, have been mainly addressed by coating them with ceramic particles. , Such ceramic coatings have been indeed adopted for commercial cells for some time.…”