Carbon network architecture controls capacity retention and self-discharge in polyimide anodes for aqueous batteries

Achieving sufficient electrochemical activity in redox-active organic materials relies on incorporating sufficient conductive carbon to establish a percolating network between the active phase and the current collector. This network is essential for enabling efficient electron transport and full active material utilization. In aqueous electrolytes, however, the same conductive carbon network can also promote parasitic aqueous reduction reactions, possibly including hydrogen evolution, which may contribute to self-discharge and capacity fade. Here, we examine how the type and loading of conductive carbon influence capacity utilization, rate capability, self-discharge, and long-term stability of polyimide (PI) anodes in aqueous electrolytes. Using carbon black (Super P) particles with different specific surface areas and carbon nanotubes (CNTs) as conductive additives, we show that increasing conductive additive loading improves PI capacity utilization and rate performance. However, higher carbon black loading and surface area also accelerate capacity fading during prolonged cycling, and enhance self-discharge through the larger electronically accessible carbon-electrolyte interface. In contrast, CNTs form efficient one-dimensional percolating conductive networks at substantially lower loadings. This enables electrons to move efficiently between polymer particles and through the polymer domains themselves, without requiring a large increase in electronically accessible carbon surface. As a result, CNT-based electrodes achieve high PI utilization and good rate capability while mitigating capacity fading and self-discharge. Long-term cycling and full-cell measurements paired with a NiPBA cathode further demonstrate improved electrode-level performance when CNTs are used as the conductive additive. These results show that improving electronic percolation by increasing carbon content can also enhance parasitic reactions at the carbon-electrolyte interface, highlighting a key trade-off in the design of aqueous polymer electrodes.