Impact-resistant supercapacitor by hydrogel-infused lattice

The study addresses the need for safe, robust supercapacitors capable of operating in harsh environments (e.g., aerospace, underwater, and high-impact scenarios). Conventional protective housings add weight and volume and do not protect internal components (electrodes and electrolytes). The authors propose reinforcing the core components themselves using load-bearing, conductive, and configurable structures to preserve functionality while improving damage resistance. Polymer-derived ceramic SiOC is identified as a strong, chemically stable, and 3D-printable substrate suitable as a current collector; its conductivity can be enhanced via graphitization/coating. Hydrogel electrolytes are considered as safer, leak-resistant alternatives to liquids, offering flexibility and possible self-healing via reversible bonds. To overcome mechanical weak points and anisotropy of traditional lamellar cells, the authors design a continuous, triply periodic minimal surface (TPMS) SiOC skeleton shared by electrodes and separator, infused with a PVA hydrogel electrolyte, to create mechanically coherent, isotropic, ready-to-use supercapacitor cells. The research question is whether such hydrogel-infused, 3D-printed SiOC lattice electrodes can deliver high electrochemical performance while withstanding impact, dynamic loading, and electrolyte damage with self-healing.

Background literature highlights: (1) Safety concerns in electrochemical storage and the need for robust separators/electrolytes and structural designs. (2) Polymer-derived SiOC ceramics exhibit high compressive strength and can be made conductive by coatings or doping; they are compatible with 3D printing for architected, lightweight structures. (3) Hydrogel electrolytes (e.g., PVA-based) can retain liquid electrolyte, provide flexibility, withstand deformation, and be endowed with self-healing via hydrogen and boric ester bonds. (4) TPMS architectures offer uniform periodicity, tunable porosity/surface area, and improved mechanical isotropy. Prior 3D-printed PANI-based supercapacitors exist, but performance under complex combined mechanical conditions (impact, cyclic loading, damage and repair) has been rarely explored. The present work integrates these threads by combining conductive TPMS SiOC collectors, in situ PANI, and self-healing PVA hydrogel into a mechanically reinforced all-in-one device and quantifies performance under extreme conditions.

Design and fabrication: Four TPMS structures (Gyroid, Diamond, Primitive, I-wrapped package [I-WP]) with unit size 2 mm and 200 µm resolution were generated (porosities: G 73.2%, D 65.2%, P 80.1%, I-WP 64.2%; specific surface areas: G 31.35, D 38.92, P 24.02, I-WP 34.95 cm²/cm³). Preforms were 3D printed by digital light processing vat photopolymerization using a photocurable-modified methyl-silsesquioxane resin, then pyrolyzed in Ar at 900 °C to form SiOC. A pyrolytic carbon coating was deposited by dip-coating PVP followed by carbonization at 1000 °C in Ar, yielding conductive C/SiOC current collectors.

Active material deposition: PANI was in situ polymerized on C/SiOC by immersing collectors in 0.05 M aniline in 0.5 M H2SO4, initiating with 0.05 M APS (equal volume) in an ice bath for 8 h, forming PANI/C/SiOC with nanorod arrays.

Electrolyte and assembly: A PVA hydrogel electrolyte was prepared by dissolving 2.00 g PVA in 10 mL 1 M H2SO4 at 85 °C, cooling, then adding 10 mL of 0.04 mol Na2B4O5(OH)4·8H2O (borax). The mixture was injected into FDM-printed PLA molds holding two PANI/C/SiOC electrodes and a pristine SiOC separator (all sharing the same TPMS). Freeze–thaw crosslinking formed the hydrogel electrolyte, integrating electrode–separator–electrolyte into self-standing cells (10×10×6 mm). Cells without TPMS (plate) and C/SiOC-only controls were also made.

Characterization: Morphology by SEM; SiOC microstructure by TEM; phases by XRD (Cu Kα); carbon microstructure by Raman; surface chemistry by XPS; FT-IR for PANI and PVA networks. Conductivity measured by four-probe on dense bars (2.0×0.5×0.1 cm). Ionic conductivity of hydrogel via EIS with carbon paper collectors.

Electrochemistry: Two-electrode configuration (0–1 V). CV at 10–100 mV/s; GCD at 1–10 mA/cm³ (for electrodes; cells evaluated separately); EIS 200 kHz–0.01 Hz. Calculations for volume-specific capacitance, energy, and power followed provided equations.

Mechanical testing and extreme-condition evaluations: Quasi-static compression (0.1 mm/min) on SiOC cubes (10×10×10 mm) and assembled cells. Three-point bending of structures (support span 15 mm). Impact tests by dropping a 200 g mass from set heights; impact energy normalized by cell volume. Dynamic loading tests applied cyclic strain 0–0.5% (0.01%/s), generating 0–18.8 MPa, with simultaneous electrochemical monitoring. Self-healing tests involved bisecting the cell through hydrogel along the electrode–separator interface, manually rejoining for 30 s, then re-measuring electrochemistry. COMSOL simulations assessed strain distributions in TPMS structures.

• Conductive and structural platform: Pyrolytic carbon coating raised conductivity from 16.3×10⁻³ S/m (SiOC) to 99.62 ± 4.52 S/m (C/SiOC). Hydrogel ionic conductivity was 16.29 S/m.
• Mechanical performance (cells with TPMS): Compressive stress and energy absorption for G, D, P, I-WP were 25.36 ± 1.27, 65.72 ± 2.28, 14.75 ± 1.06, and 70.61 ± 1.53 MPa; and 29.49 ± 1.59, 90.40 ± 2.65, 10.76 ± 1.14, and 92.15 ± 3.78 kJ/m³, respectively. I-WP exhibited Young’s modulus of 2.75 GPa. Three I-WP cells in series lit an LED under 10 MPa load.
• Electrochemical performance (static): Volume-specific capacitances at 3 mA/cm³ were G 516.99, D 601.06, P 369.45, I-WP 585.51 mF/cm³; plate PANI/C/SiOC 91.77 mF/cm³; C/SiOC 13.95 mF/cm³. I-WP electrode achieved 97.63 µWh/cm³ at 0.5 mW/cm³ and 62.07 µWh/cm³ at 5 mW/cm³. Cells delivered 32.54 µWh/cm³ at 0.17 mW/cm³ and 20.69 µWh/cm³ at 1.7 mW/cm³.
• Post-impact (0.3 J/cm³) performance: CV/GCD/EIS essentially unchanged; I-WP electrode specific capacitances were 699.83, 640.03, 582.54, 537.27, 478.85, and 430.18 mF/cm³ at 1, 2, 3, 5, 8, and 10 mA/cm³, respectively. Damage appeared at 0.4 J/cm³.
• Under dynamic loading (0–18.8 MPa): Electrochemical curves and capacitance/EIS showed negligible variation compared with static state.
• Self-healing of hydrogel: Cell bisected through the hydrogel rejoined within 30 s, retaining most capacitance; slight reduction attributed to electrolyte loss and increased internal resistance. After 5000 cycles at 10 mA/cm³, capacitance retention was 80.31% (83.86% at 1000 cycles). Structural analyses indicated PANI nanorod morphology changes as main cause of fade; C/SiOC did not participate in redox.
• Architecture–mechanics link: TPMS SiOC (especially I-WP and D) showed uniform strain distribution and higher specific compressive stress; continuous SiOC skeleton distributed loads and reduced stress concentration. Hydrogel retained fragments upon fracture, mitigating secondary damage.
• Lightweight design: C/SiOC densities for G, D, P, I-WP were 0.73, 0.92, 0.99, 0.50 g/cm³; lower than traditional Ni-based porous collectors, aiding gravimetric performance.

The results demonstrate that integrating a continuous TPMS SiOC skeleton with a self-healing PVA hydrogel electrolyte and in situ PANI active layers yields a supercapacitor that maintains electrochemical function under impact, dynamic mechanical loading, and after electrolyte damage. The SiOC lattice, reinforced by a conductive pyrolytic carbon coating, provides high load-bearing capability and isotropic mechanical response, dispersing stress and protecting internal components. The PVA hydrogel’s flexibility and adhesion preserve electrode–electrolyte interfaces during deformation and, via reversible hydrogen and boric ester bonds, enables rapid self-repair of the ionic pathway after damage. PANI nanorod arrays increase accessible surface area and facilitate fast redox transitions (LB/EB/PB), supporting high volumetric capacitance and rate capability. Minimal deviations in CV, GCD, and EIS between static and stressed states confirm that the architecture effectively decouples mechanical insults from electrochemical pathways. Compared to conventional lamellar cells and prior 3D-printed PANI devices, the approach adds demonstrable resilience to extreme conditions while remaining lightweight and scalable. The architecture’s tunability via TPMS selection allows balancing surface area, porosity, and mechanical properties to optimize device performance for targeted applications.

This work establishes a fabrication strategy for ready-to-use, impact-resistant, load-bearing, and self-healing supercapacitors by combining 3D-printed TPMS SiOC lattices (as conductive current collectors and structural skeletons), in situ PANI active layers, and PVA–H2SO4–borax hydrogel electrolytes. The I-WP architecture delivered high volumetric capacitance (585.51 mF/cm³ at 3 mA/cm³) and energy density (up to 97.63 µWh/cm³ at 0.5 mW/cm³) while achieving strong mechanical metrics (compressive stress 70.61 MPa, modulus 2.75 GPa, energy absorption 92.15 kJ/m³). The device preserved electrochemical functionality after 0.3 J/cm³ impact, during cyclic loading up to 18.8 MPa, and after self-healing. The continuous SiOC lattice ensures uniform load distribution; hydrogel bonds enable fast repair; and PANI nanostructuring supports stable redox. The approach is scalable via vat photopolymerization and adaptable to varied device geometries and connection schemes (including interlocking features). Future work should enhance temperature tolerance (anti-freezing and anti-drying) and further improve long-term cycling stability, and could extend the structurally strengthened concept to other active materials and electrolyte systems.

• Impact threshold: Cells remained intact up to 0.3 J/cm³; visible SiOC damage occurred at 0.4 J/cm³.
• Cycling stability: Capacitance declined to 83.86% after 1000 cycles and 80.31% after 5000 cycles at 10 mA/cm³, mainly due to PANI surface morphology changes.
• Hydrogel vulnerabilities: PVA hydrogel can lose electrolyte during damage/healing, increasing internal resistance and slightly reducing capacitance; authors note the need for improved temperature adaptability (anti-freezing and anti-drying).
• Mechanical variations among architectures: Some TPMS cells (e.g., Diamond) showed larger mechanical performance drops post-assembly, likely from defects induced by pyrolysis shrinkage and hydrogel freeze–thaw expansion.
• Slight reduction in compressive strength from substrate to assembled cells due to hydrogel-related defects.
• Study focuses on symmetric PANI-based systems; broader chemistries and environmental extremes (temperature, long-term humidity) remain to be validated.