Rechargeable Li-metal batteries (LMBs) are conceivably one of the most promising battery technologies to achieve high energy densities for sustainable transport applications and grid-storage components. Electrolytes are a critical component of a battery that allows the ion-transport for the efficient charge-discharge of the battery. Conventional liquid electrolytes (e.g. a mixture of lithium salt and alkyl carbonates) that are employed in a typical Li-ion battery are flammable. Moreover, they can also react with the Li-metal, leading to irreversible reactions and dendrite formation on the lithium metal surface. Solid polymer electrolytes (SPEs) have been reported to limit this reactivity, however their low ionic conductivities at room temperature (<10−4 S/cm) have impeded their use in a rechargeable LMB device for ambient temperature operation. This dissertation describes the synthesis, characterization, and applications of new solid polymer electrolytes for lithium battery applications with main emphasis on using poly(ethylene oxide) (PEO) as the ionically conducting segment and semi-crystalline polymers, namely polyethylene (PE) and syndiotactic polypropylene (sPP) as the mechanically rigid segments. We developed a new class of PE/PEO cross-linked polymer electrolytes using ring opening metathesis polymerization route. These SPEs demonstrated both high ionic conductivity (>10−4 S/cm at 25 °C) and unprecedented levels of dendrite growth resistance. We also formulated new SPE compositions by varying the lithium salts and the plasticizers in these PE/PEO cross-linked systems. To achieve better transport properties, we synthesized Li-ion conducting network polyelectrolytes that contained non-coordinating tetraphenylborate anions tethered to the polyethylene backbone. We also developed syndiotactic polypropylene-b-poly(ethylene oxide)-b-syndiotactic polypropylene (PEOP) triblock copolymers using azide-alkyne “click” chemistry route. PEOP triblock copolymers containing different block sizes were synthesized and doped with a lithium salt for use as an electrolyte in a lithium battery. Finally, we established structure-property relationships for several SPEs reported in this dissertation. We anticipate that some of the polymer electrolytes described in this work will provide useful insights for the design of SPEs with superior electrolyte properties, including higher ionic conductivity, better electrochemical stability, and excellent dendrite growth resistance.