NASA future missions demand safe, high specific energy (>400 Wh/kg) batteries. Current state-of-the-art (SOA) lithium-ion batteries (LIBs) can only provide ~150-200 Wh/kg in energy capacity, which is unable to meet NASA's future energy goals, and also pose safety issues due to the use of liquid flammable electrolyte. There are intense on-going development activities to increase battery energy density. Among the promising next generation high energy battery chemistries are lithium/sulfur (Li/S) and lithium oxygen (Li/O2), in which lithium metal is used as the common anode. The use of Li metal as an anode material has emerged as one highly attractive option for achieving high-energy, next generation batteries. This is because Li has many advantages. It is the lightest metal, but also has the highest theoretical capacity (3876 mAh/g). It also has the lowest potential (0V), which boosts whole cell voltage, and Li metal is 100% active material and requires no binder. Thus, Li metal is an ideal anode material for high energy battery chemistries. However, the reliable use of this exceptionally high capacity anode in a commercial rechargeable battery has not been achieved due to safety and reliability concerns resulting from thermal runaway and short-circuit issues due to dendritic growth on the Li metal anode from lithium plating during charge-discharge cycles. The solid polymer nanocomposite electrolyte (SPNE) has been identified as a promising option to address lithium metal cycling safety. The SPNE is non-flammable and, by replacing the liquid flammable electrolyte, it eliminates leakage and fire hazard, in addition, it provides flexibility of design. This proposed solid polymer nanocomposite electrolyte addresses the challenges of achieving both high energy and safety for next generation battery. However, the SPNE technology must be developed to possess high conductivity, and thermal and mechanical properties conducive to robust Li metal cycling safely. The goal is to maximize ionic conductivity, thermal and mechanical properties of the solid polymer nanocomposite electrolyte (SNPE) film by optimizing compositions, and identify the maximum current density for depressing Li dendrites for safe Li cycling.