Solid-State Hybrid Electrolytes Based on Surface-Functionalized Nanoparticles and Nitrile Materials

Abstract

Lithium ion batteries (LIBs) have been extensively investigated as one of the popular energy storage systems for various electronic devices due to high energy densities, no memory effect, long lifetime and slow self-discharge rate. However, recently, LIBs are facing crucial safety issues prompted by highly flammable characteristics of liquid electrolytes. Possible reasons of safety issues include exothermic reactions and the mechanical/ thermal instability of battery separator causing an internal short circuit. The need for non-flammable and mechanically robust electrolytes to replace existing commercial liquid variants is thus rapidly emerging. In order to improve mechanical/ thermal properties, composite polymer electrolytes (CPEs), a variety of hybrid electrolyte designs that include embedded inorganic nanofillers, have been widely studied. Due to the insulating nature of inorganic nanoparticles, the development of mechanically robust CPEs without any loss of ion transport properties is of paramount importance.

In this study, I investigated a unique, highly conductive, dendrite-inhibited, solid-state polymer electrolyte platform that demonstrates excellent battery performance at subzero temperatures. A design based on functionalized inorganic nanoparticles with interconnected mesopores that contain surface nitrile groups is the key to this development. Solid-state hybrid polymer electrolytes based on succinonitrile (SN) electrolytes and porous nanoparticles were fabricated via a simple UV-curing process. SN electrolytes were effectively confined within the mesopores. This stimulated favorable interactions with lithium ions resulted on improved lithium dissociation and ionic conductivities. In particular, the confinement effects by surface functionalized pores of silica nanoparticles offered enhanced thermodynamic compatibility with SN, leading to reduced leakage of SN electrolytes over time and improved mechanical strength of membranes. Inhibition of lithium dendrite growth and improved electrochemical stability up to 5.2 V were also demonstrated. The hybrid electrolytes exhibited high ionic conductivities of 2 ×10−3 S cm-1 at room temperature and > 10-4 S cm-1 at subzero temperatures, leading to stable and improved battery performance at subzero temperatures. Li cells made with lithium titanate anodes exhibited stable discharge capacities of 151 mAh g-1 at temperatures below -10 oC. This corresponds to 92% of the capacity achieved at room temperature (164 mAh g-1). This work represents a significant advance in solid-state polymer electrolyte technology and far exceeds the performance available with conventional polymeric battery separators.