Highly Compressible Graphene/Polyaniline Aerogel: Superelasticity Meets 713 F g⁻¹ Capacitance for All‑Solid‑State Supercapacitors

Background

Portable and wearable electronics demand energy‑storage solutions that can withstand significant mechanical deformation, especially compression. Supercapacitors (SCs) excel in power density, rapid charge–discharge rates, and cycle life, making them ideal for such applications. However, most existing SC electrodes only recover 50–75 % of their volume after compression, which limits practical deployment.

Superelastic graphene aerogels, characterized by honeycomb‑like or bubble‑structured pores, can recover 90–99 % of their volume. Their high compressibility stems from tightly integrated multilayer graphene walls and an ordered pore network. Despite this mechanical advantage, their specific capacitance is limited (37–90 F g⁻¹) because of the double‑layer storage mechanism inherent to carbon.

Integrating pseudocapacitive materials—such as Co₃O₄, MnO₂, PANI, or PPy—into graphene aerogels can enhance capacitance. Prior studies with MnO₂ achieved only 106 F g⁻¹ and 50 % strain, largely due to weak particle adhesion. PANI, with strong π–π interactions to graphene and high pseudocapacitance, presents a promising route to overcome this limitation.

In this work, we deposit PANI onto a superelastic graphene aerogel via cyclic voltammetry, creating a composite that preserves the scaffold’s elasticity while adding substantial pseudocapacitance. The resulting electrode demonstrates outstanding mechanical resilience and electrochemical performance, as verified in all‑solid‑state SCs.

Methods/Experimental

Preparation of Superelastic Graphene Aerogel

Graphene oxide (GO) was synthesized by the modified Hummers’ method. Using the ice‑template approach, a GO dispersion (5 mg mL⁻¹) was mixed with L‑ascorbic acid, reduced at 90 °C, freeze‑thawed, and further reduced to yield a fully reduced graphene hydrogel. Dialysis and drying at 60 °C produced the superelastic aerogel.

Preparation of Superelastic Graphene/PANI Aerogel

PANI was electrochemically polymerized onto the aerogel by cyclic voltammetry (–0.2 to 0.8 V, 50 mV s⁻¹) for 100–400 cycles in 1 M H₂SO₄/0.05 M aniline. The mass fraction of PANI was determined from pre‑ and post‑deposition weights. For example, 200 cycles (Graphene/PANI‑2) yielded a 63 wt % PANI loading.

Fabrication of Compressible All‑Solid‑State SCs

Electrolyte gel (PVA/H₂SO₄) was prepared (4:5:50 mass ratio) and stirred at 80 °C. Aerogels were soaked for 30 min, then assembled between PET substrates coated with 100 nm Au. A Celgard 3501 separator saturated with the gel completed the sandwich, which was pressed and cured at 45 °C for 24 h.

Materials Characterization

Raman spectroscopy, SEM/EDS, FTIR, XPS, and compression testing (Instron‑5566, 100 mm min⁻¹) were used to analyze structure, composition, and mechanical response.

Electrochemical Measurements

CV, GCD, and EIS were performed with a CHI660E workstation. Specific capacitance (C_s) was derived from GCD data: C_s = I·Δt/(m·ΔV). In the two‑electrode SC, gravimetric (C_g) and volumetric (C_vol) capacitances were calculated using the equations C_g = 4IΔt/(mΔV) and C_vol = ρC_g, where ρ is the aerogel density under compression.

Results and Discussion

The fabrication flow is illustrated in Figure 1. The ice‑templated reduction yields a honeycomb‑structured, highly porous aerogel with graphene sheets tightly stacked to form robust cell walls (Figure 2). The ordered architecture provides both elasticity and a high surface area.

SEM images (Figure 3) confirm that the PANI grows as uniform nanocones along the cell walls, preserving the aerogel’s morphology. Up to 300 CV cycles, the coating remains conformal; beyond this, excessive PANI forms a nanowire network that can detach during washing.

FTIR (Figure 4a) shows characteristic PANI peaks (C=C, C–N, and C–H vibrations), while XPS confirms successful doping of PANI with sulfate ions. The high N⁺ ratio indicates a highly protonated, conductive state.

Compression tests (Figure 5) reveal that Graphene/PANI‑2 recovers 90 % strain with no residual deformation and reaches a peak stress of 131 kPa at 90 % strain—higher than the unmodified aerogel (36 kPa). Even after 500 cycles at 60 % strain, the material retains its structural integrity with only a 5 % residual strain.

Electrochemical tests (Figure 6) show that the PANI‑functionalized aerogel delivers a specific capacitance of 713 F g⁻¹ at 1 A g⁻¹, the highest among the tested composites. The capacitance retention at 10 A g⁻¹ is 82 %, and the cycling stability is 92 % after 1,000 GCD cycles.

In solid‑state SCs, the graphene/PANI‑2 electrodes maintain 424 F g⁻¹ gravimetric capacitance and 65.5 F cm⁻³ volumetric capacitance at zero strain, and retain 96 % of these values under 90 % compression. The volumetric capacitance rises to 85.5 F cm⁻³ at 90 % strain, owing to the increased density while preserving most of the gravimetric capacity.

Long‑term cycling under static and dynamic compression shows minimal capacitance loss (≈ 9 % after 1,000 cycles). Ragone analysis yields a peak energy density of 9.4 W h kg⁻¹ at 0.4 kW kg⁻¹ power density.

To overcome the low voltage of a single cell, three SCs were connected in series via Au patterning on PET. The integrated device operated at 2.4 V, powering a red LED even during repeated compression and release cycles (Figure 8).

Conclusions

Electrochemical deposition of PANI onto a superelastic graphene aerogel creates a composite that simultaneously offers 90 % recoverable strain and a specific capacitance of 713 F g⁻¹. In all‑solid‑state SCs, the electrodes deliver 424 F g⁻¹ and 85.5 F cm⁻³ under 90 % compression, outperforming other compressible composites. The ability to connect multiple units in series further expands the operating voltage, enabling practical power delivery for flexible electronics. This work establishes a robust platform for next‑generation, compression‑tolerant energy‑storage devices.