The development of the lithium-ion battery has played an indispensable role in shaping the landscape of portable electronics and emerging electric vehicle industry. While its development has been recognized with a Nobel Prize in 2019, battery technology is far from mature. Since its conception, the battery research landscape has only widened with the rise of electric vehicles and wearable devices, each having a different set of requirements. Therefore, the “next-generation” in the context of this dissertation focuses on two different aspects of the battery field. The first aspect considers the development of high energy density batteries and more specifically the move away from capacity-limited intercalation chemistries. Chapter 3 delves into the interfacial challenges posed by lithium metal anodes during the Li plating/stripping reactions while Chapter 4 visits the complex reaction pathways in FeS2 conversion cathodes to understand charge product formation and identify capacity loss mechanisms. While both Li and FeS2 are commercialized as primary battery electrode materials and have the potential to provide high energy density rechargeable batteries, safety and performance issues have limited their use to primary systems. Ultimately, better understanding of the interfaces and reaction pathways can fuel the design of solutions to improve the performance and safety of these systems. The latter part of the dissertation focuses on the other type of “next-generation” battery, namely, that of miniaturized power sources for IoT technologies. With the vision of an on-chip battery integrated into a device, new materials and processes must be developed to integrate the same semiconductor processing techniques used to make the device to make the batteries as well. Chapter 5 details the development of a conformal, photopatternable separator and the integration of the separator onto various battery architectures. The ability to spatially photopattern a porous separator onto three dimensional architectures provides a path towards high power on-chip batteries. In summary this dissertation aims to provide perspective in the different directions and progress towards the next generation of rechargeable batteries. From better fundamental insights on complex electrochemical pathways to application-driven materials design and development, this dissertation highlights a few of the challenges, discoveries, and advancements of a much larger research landscape of “next-generation” batteries.