Flexible pseudocapacitor operates in extreme temperatures, stores high energy

(Nanowerk Spotlight) Electricity powers our modern world, from everyday electronics to critical infrastructure. As devices become more advanced and ubiquitous, there is an urgent need for safe, compact, high-performance energy storage solutions that can function reliably in any environment. Batteries have long been the dominant technology, offering high energy density. However, they suffer from safety issues, limited power output, and reduced performance in extreme temperatures.
Capacitors, which store energy in electric fields, provide high power and durability but cannot match batteries' energy density. For decades, scientists have sought to combine the best of both, developing hybrid devices known as pseudocapacitors.
A pseudocapacitor is a type of electrochemical capacitor that bridges the gap between conventional capacitors and batteries. It stores charge through rapid, reversible redox reactions occurring at the surface of its electrodes, which are typically made from nanostructured materials with high surface areas. This pseudocapacitive charge storage mechanism enables pseudocapacitors to achieve battery-like energy densities while maintaining the high power and long lifetimes characteristic of capacitors.
Pseudocapacitors that perform reliably in the coldest and hottest environments could power wearable electronics, remote sensors, and exploration equipment in the harshest conditions. They may find applications in space missions, high-altitude drones, subsea monitoring, and oil and gas operations.
Moreover, the modular and scalable nature of pseudocapacitors makes them attractive for grid-scale energy storage. By buffering the intermittent output of wind and solar farms, they could help accelerate the transition to a carbon-neutral energy system. Their rapid charging and discharging capabilities are also ideally suited for regenerative braking in electric vehicles and trains, improving energy efficiency.
Pseudocapacitors utilize electrodes made from nanostructured materials that undergo fast, reversible redox reactions at their surface. This pseudocapacitive charge storage mechanism, akin to that in batteries, boosts energy density while preserving the characteristic high power and longevity of capacitors.
"Progress in pseudocapacitor development has been hindered by the lack of suitable electrode materials and electrolytes," Dr. Debasis Ghosh, Assistant Professor at the Centre for Nano and Material Sciences, Jain University, India, explains to Nanowerk. "Most aqueous electrolytes have narrow electrochemical stability windows, restricting operating voltages. Organic electrolytes widen the voltage range but introduce flammability risks. Ionic liquids are expensive and often too viscous for practical use. On the electrode front, transition metal oxides offer attractive capacities but struggle with low conductivity, structural degradation, and inefficient ion transport."
In recent years, breakthroughs in materials science and engineering have reignited hope for high-performance pseudocapacitors. Nanostructuring techniques can now craft electrode materials with vast surface areas, facilitating rapid charge transfer. Pioneering "water-in-salt" electrolytes, which utilize high salt concentrations, push aqueous stability limits to battery-like voltages. Flexible current collectors and innovative device architectures pave the way for integrating pseudocapacitors into wearable electronics and compact applications. The stage is set for a new generation of safe, versatile, and long-lasting energy storage solutions.
A team of scientists from several institutions in India and South Korea have taken a significant stride toward this goal. The work was led by Dr. Debasis Ghosh (Principal Investigator) and Dr. Hyunyoung Jung, an Associate Professor of Energy Engineering at Gyeongsang National University in Korea. In a study published in the journal Small ("A 2.5 V In-Plane Flexi-Pseudocapacitor with Unprecedented Energy and Cycling Efficiency for All-Weather Applications"), they present a groundbreaking flexible pseudocapacitor that maintains exceptional performance across an unprecedented temperature range of -40 °C to 60 °C. This all-climate device opens new avenues for energy storage in extreme environments, from aerospace to deep sea exploration.
Schematic of the fabrication of interdigitated V5O12·6H2O @LSC electrodes
a) Schematic of the fabrication of the interdigitated V5O12·6H2O @LSC electrodes, b) XRD, and c) Raman analysis of the V5O12·6H2O @LSC; High-resolution deconvoluted XPS spectra of d) V 2p and e) O 1s of the V5O12·6H2O. (Image: reprinted with permission by Wiley-VCH Verlag)
At the heart of this innovation lies a novel electrode material: vanadium oxide (V5O12·6H2O) electrodeposited onto laser-scribed graphene. The researchers used a rapid, scalable laser scribing technique to convert polyimide sheets into porous, conductive graphene electrodes. This 3D network provides abundant surface area and efficient charge transport pathways for the active vanadium oxide layer. Crucially, the open porous structure allows unimpeded electrolyte access, maximizing ion transport even at subzero temperatures.
Complementing the electrode is a carefully tuned "water-in-salt hybrid" electrolyte. The scientists combined a high concentration of sodium perchlorate salt (17m NaClO4) with an ethylene glycol-water mixture. This unique formulation pushes the electrochemical stability window to 2.6V, approaching that of organic electrolytes. The ethylene glycol acts as an antifreeze, allowing the electrolyte to remain liquid and conductive down to -40 °C. Molecular dynamics simulations revealed how the hybrid electrolyte structure and hydrogen bonding evolve with temperature, helping explain its remarkable low-temperature performance.
The assembled pseudocapacitor showcased extraordinary energy storage capabilities. At room temperature and a current density of 1 A/g, it achieved an areal capacitance of 234.7 mF/cm2, corresponding to a high energy density of 203.7 µWh/cm2. Impressively, the device maintained a capacitance of 129.8 mF/cm2 at -40 °C, a temperature where most batteries and supercapacitors fail. The capacitance increased dramatically at elevated temperatures, reaching 116.2 mF/cm2 at 60 °C. Electrochemical impedance spectroscopy measurements confirmed fast ion diffusion across the entire temperature range.
"Our long-term stability testing further highlighted the pseudocapacitor's robustness," Ghosh points out. "After 80,950 charge-discharge cycles at room temperature, it retained 76% of its initial capacitance, indicating minimal degradation."
Notably, he adds, the device showed consistent and reproducible performance when subjected to repeated thermal cycling between -40 °C, room temperature, and 60 °C. It also demonstrated excellent mechanical flexibility, with negligible capacitance loss under bending stresses.
Beyond its impressive performance metrics, this work showcases the power of rational materials design and multidisciplinary collaboration. By synergistically optimizing the electrode structure, electrolyte composition, and device architecture, the team achieved a leap in pseudocapacitor capabilities. Their holistic approach, guided by computational simulations, underscores the importance of fundamental understanding in developing next-generation energy storage solutions.
While challenges remain in scaling up production and further improving energy density, this study provides a compelling proof-of-concept for all-climate pseudocapacitors. It sets the stage for a new wave of research into electrode materials, electrolyte formulations, and device designs that can push the boundaries of energy storage performance. With sustained progress, flexible pseudocapacitors may soon become the versatile, long-lasting power source our increasingly electrified and interconnected world demands.
Michael Berger By – Michael is author of three books by the Royal Society of Chemistry:
Nano-Society: Pushing the Boundaries of Technology,
Nanotechnology: The Future is Tiny, and
Nanoengineering: The Skills and Tools Making Technology Invisible
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