Spatial Distribution Control on the Energy Storage Performance of PANI@PVA@ACNT-Based Flexible Solid-State Supercapacitors

In this work, a redox and an electrochemical polymerization method were carried out separately to produce the composite PANI@PVA@ACNT-based flexible solid-state supercapacitor (FSC) device with symmetrical "sandwich structure". Interestingly different polymerization methods result in different spatial structures, which lead to significant difference in the ion transport behaviors and energy storage mechanisms. The redox-polymerized aniline (R-PANI) provides a 3D polyaniline network in the gel system which exhibits a diffusion-controlled energy storage mechanism. While the electrochemical-polymerized aniline (E-PANI) is found to form a PANI nanoparticles attached-CNTs structure which shows a more typical pseudocapacitive behavior and better rate performance. The maximum specific capacitance of the E-PANI@PVA@ACNT and R-PANI@PVA@ACNT device reached as high as 896 mF·cm–3 (206 mF·cm–2) and 667 mF·cm–3 (200 mF·cm–2) respectively, which is much better than the prepolymerized PANI@ACNT samples (216 mF·cm–3). In addition, the composite devices based on highly densified carbon nanotube arrays (DACNTs) were found to have a superior electrochemical performance. The maximum specific capacitance of the E-PANI@PVA@DACNT and R-PANI@PVA@DACNT device reached as high as 1.95 F·cm–3 (432 mF·cm–2) and 2.91 F·cm–3 (873 mF·cm–2), respectively. The highest energy density was measured to be 0.389 mW·h·cm–3 (0.09 mW·h·cm–2) for E-PANI@PVA@DACNT and 0.572 mW·h·cm–3 (0.17 mW·h·cm–2) for R-PANI@PVA@DACNT with high power density of 11.2 mW·cm–3 (2.58 mW·cm–2) and 74.4 mW·cm–3 (22.3 mW·cm–2), respectively. Besides, the long-term cyclic stability and excellent rate performance of such devices were also achieved. Our approach well overcomes the general obstacle that the hydrogel electrolyte is likely blocked by the carbon-based electrode materials in the FSC system. In addition, our findings reveal that the relationship between the spatial distribution and energy storage mechanisms of mixed-type supercapacitor devices thus helps the design of redox-enhanced FSC devices with excellent performances.