Researchers from China University of Petroleum (East China), Henan Agricultural University and Chinese Academy of Sciences have developed an additive-free 3D printing process to construct graphene micro-supercapacitors (MSCs) with unprecedented electrochemical properties and seamless integrability. The team states that this achievement overcomes existing manufacturing limitations and brings closer the on-chip MSC arrays essential for the next generation of wearables.
Wearable devices require ever-smaller on-board energy solutions that can deliver bursts of power while remaining unobtrusive. Rigid coin batteries restrict device flexibility and ergonomics. Leading microscale alternatives include micro-supercapacitors (MSCs), which store and discharge energy rapidly owing to highly porous electrode materials interfacing with electrolytes. Supercapacitors’ quick charge ability and resilience to repeated charging cycles make them appealing to supplement batteries. However, difficulties producing intricately designed MSC devices that also offer high performance have confined MSCs to the lab. Conventional manufacturing techniques often lack suitable precision, flexibility, and scalability.
Graphene can serve as an ideal MSC electrode material, but dispersing pristine graphene into printable inks has proven difficult. Researchers frequently rely on graphene oxide strategies, adding various performance-inhibiting chemicals to control ink rheology. The subsequent requirement for post-printing chemical reduction further increases complexity.
The new research demonstrates an additive-free graphene ink with exceptional printability, allowing intricate MSC electrode architectures to be 3D printed without any freezing or post-processing. Key to the breakthrough was an electrochemical exfoliation technique that yields high-quality, few-layer graphene sheets with enhanced edge plane exposure. These graphene nanosheets could be dispersed into a simple glycerin/water solution to create a moderate viscosity ink tailored for extrusion-based 3D printing.
Printing with the novel ink enabled construction of MSCs with an ultrasmall footprint down to 0.025 cm2. The pure graphene electrodes delivered exceptional electrochemical performance, including a remarkable areal capacitance of 4900 mF cm−2 and volumetric capacitance of 195.6 F cm−3 – surpassing most other printed MSCs.
An optimized MSC architecture printed with 10 layers achieved an unprecedented areal energy density of 2.1 mWh cm−2 and volumetric energy density of 22 mWh cm−3. Testing proved excellent cycling stability, with 83% capacitance retention after 10,000 cycles.
Manufacturing scalability was demonstrated by 3D printing a MSC array with 90 closely integrated cells within a 5.625 cm2 area. Strong performance uniformity between cells enabled integration into high-voltage stacks exceeding 190 V – the highest output achieved for printed MSCs. The team printed an exceptional maximum of 16 cells per cm2, showing the potential for tailoring large MSC assemblies.
The customizability afforded by additive-free graphene 3D printing provides exciting opportunities to explore and optimize MSC designs. The researchers validated quality printing of interdigitated electrodes in diverse architectures, wireless charging coils, and snowflake-like patterns. Hybrid devices with integrated MSC arrays and other printed components can now be constructed to meet the power demands of microelectronics innovations like lab-on-a-chip biosensors and flexible displays.
While demonstrating considerable progress, questions remain before additive-free graphene 3D printing can enable commercial micro-supercapacitors. The considerable volatility and flammability of commonly used electrolytes may restrict applications. Acquiring specialized equipment for extrusion-based printing could pose financial barriers for wider adoption. And graphene ink production must scale cost-effectively.
Additionally, the printing resolution and minimum feature size achievable may not yet reach that of photolithography. Long-term durability exceeding 100,000 cycles also requires further improvement for competitive commercial lifespan. Future work should quantify precise manufacturing costs per device and explore mitigating toxicity concerns around certain electrolyte compositions. Still, the considerable customizability and electrochemical performance advances show great promise to empower creative MSC designs.
Real-world demonstration showed a MSC successfully powering a 42 LED light display. With scalability to industrial-level production, the proposed technique offers a pathway to finally actualize graphene MSCs as a disruptive microscale energy storage solution ready for integration across stretchable electronics applications. Looking beyond energy storage, the robust and high-resolution 3D printing ability open possibilities for graphene-based devices in medical, energy, and computing domains.