A Cross‐linked n‐Type Conjugated Polymer with Polar Side Chains Enables Ultrafast Pseudocapacitive Energy Storage

Abstract

Pseudocapacitors bridge the performance gap between batteries and electric double‐layer capacitors by storing energy via a combination of fast surface/near‐surface Faradaic redox processes and electrical double‐layer capacitance. Organic semiconductors are an emerging class of pseudocapacitive materials that benefit from facile synthetic tunability and mixed ionic‐electronic conduction. Reported examples are mostly limited to p‐type (electron‐donating) conjugated polymers, while n‐type (electron‐accepting) examples remain comparatively underexplored. This work introduces a new cross‐linked n‐type conjugated polymer, spiro‐NDI‐N, strategically designed with polar tertiary amine side chains. This molecular design aims to synergistically increase the electroactive surface area and boost ion transport for efficient ionic‐electronic coupling. Spiro‐NDI‐N demonstrates excellent pseudocapacitive energy storage performance in pH‐neutral aqueous electrolytes, with specific capacitance values of up to 532 F g⁻¹ at 5 A g⁻¹ and stable cycling over 5000 cycles. Moreover, it maintains a rate capability of 307 F g⁻¹ at 350 A g⁻¹. The superior pseudocapacitive performance of spiro‐NDI‐N, compared to strategically designed structural analogues lacking either the cross‐linked backbone or polar side chains, validates the essential role of its molecular design elements. More broadly, the design and performance of spiro‐NDI‐N provide a novel strategy for developing high‐performance organic pseudocapacitors.