Block Copolymer-derived Porous Polyimides and Carbon for High-Performance Energy Storage

Block copolymer-derived nanoporous materials are featured with microstructures defined by the microphase separation of constituent blocks, enabling various applications in energy storage. Dictated by the molecular weights and volume fractions of constituent blocks, the microphase separation forms nanoscale microstructures of 1-100 nm. Selective removal of a sacrificial phase produces nanopores with tailored pore width, continuity, and tortuosity. The remaining phase customizes the properties of resulting nanoporous materials, including specific surface area, electrical conductivity/insulation, and mechanical performance. Therefore, block copolymer-derived porous materials are felicitous for use in high-performance energy storage. This dissertation presents the utilization of block copolymers to derive nanoporous materials: i) high-modulus polyimide separators for lithium-metal batteries, and ii) high-surface-area carbon electrodes for fast-charging zinc-ion batteries. In lithium-metal batteries, the dendritic growth of lithium leads to deteriorating performance and severe safety concerns. Suppressing lithium dendrites is imperative to guarantee both high performance and safe cycling. Mesoporous polyimide separators are promising for dendrite suppression: i) the mesopores are smaller than the width of lithium dendrites, preventing lithium dendrites from penetrating the separator. ii) The high-modulus polyimide ceases the growth of lithium dendrites. Herein, this dissertation reports a mesoporous polyimide separator produced by thermalizing polylactide-b-polyimide-b-polylactide at 280 °C. The mesoporous polyimide separator exhibits a median pore width of 21 nm and a storage modulus of 1.8 GPa. When serving as a dendrite-suppressing separator in lithium-metal batteries, the mesoporous polyimide separator enables safe cycling for 500 hours at a current density of 4 mA/cm2. In zinc-ion batteries, developing cathodes compatible with fast charging remains a challenge. Conventional MnO2 gravel cathodes suffer from low electrical conductivity and slow ion (de-)insertion, resulting in poor recharging performance. In this dissertation, porous carbon fiber (PCF) supported MnO2 (PCF@MnO2), comprising nanometer-thick MnO2 deposited on block copolymer-derived PCF, serves as a fast-charging cathode. The high electrical conductivity of PCF and fast ion (de-)insertion in nanometer-thick MnO2 both contribute to a high rate capability. The PCF@MnO2 cathode, with a MnO2 loading of 59.1 wt%, achieves a MnO2-based specific capacity of 326 and 184 mAh/g at a current density of 0.1 and 1.0 A/g, respectively. This dissertation investigates approaches to utilizing block copolymers-derived nanoporous materials for high-performance energy storage. Those approaches are envisaged to inspire the design of block copolymer-derived nanoporous materials, and advance the development of "beyond Li-ion" energy storage.