Imagine a smartphone with a protective case that also acts as a battery or an electric car that uses its doors and floorboard to store and supply power. These are some of the futuristic applications of a new device developed by engineers at the University of California San Diego.
Structural supercapacitor
The device is called a structural supercapacitor, and it can do two things at once: provide mechanical support and store electrical energy. This means it can make electronic devices and vehicles more robust and durable without adding extra weight.
Structural supercapacitors are not a new idea, but they have been challenging. Most supercapacitors are good at storing energy but are too weak to be used as structural materials. On the other hand, most structural materials are strong enough to support loads. However, they could be better at storing energy.
A team of researchers led by professors Tse Nga (Tina) Ng and Xinyu Zhang from the Department of Electrical and Computer Engineering at UC San Diego has solved this problem by creating a structural supercapacitor that excels at both functions. They reported their work in Science Advances.
To demonstrate their invention, the researchers built a small solar-powered boat using their structural supercapacitor. They shaped the supercapacitor into the boat's hull and attached a motor and a circuit. The circuit was connected to a solar cell, which charged the supercapacitor when exposed to sunlight. The supercapacitor powered the motor, allowing the boat to sail on water. This showed how the device can be used as a structure and a battery.
The device comprises standard supercapacitor components: two electrodes separated by an electrolyte, which allows ions to move between them. What makes the device special is its choice of materials that enhance its strength and performance.
The electrodes are made of carbon fibers woven into a fabric, which gives them high mechanical strength. They are coated with a conductive polymer mixture and reduced graphene oxide, improving their ion flow and energy storage capacity.
The electrolyte is a solid material that consists of epoxy resin and polyethylene oxide, another conductive polymer. The epoxy resin provides structural support, while the polyethylene oxide creates pores that enable ion mobility.
The clever part of the design is that the amount of polyethylene oxide varies across the electrolyte, creating concentration gradients. The areas near the electrodes have more polyethylene oxide, which helps ions move faster and more efficiently at the interface, increasing performance. The rooms in the middle have less polyethylene oxide, which reduces pores and strengthens the material. This way, the electrolyte balances both functions.
Ng explained that this gradient configuration is the key to achieving optimal performance in the electrolyte. "We designed it so that the edges that touch the electrodes have higher electrical performance while the middle is mechanically stronger," she said.
Future work
While this represents a significant advancement toward structural energy storage, the researchers note that much work still needs to be done. Supercapacitors generally have high power density, meaning they can quickly deliver big bursts of energy. However, they typically have lower energy density compared to batteries.
The study's first author, Lulu Yao, a Ph.D. student in materials science and engineering working in Ng's lab, emphasized that their future efforts will concentrate on enhancing the energy density of their supercapacitor to make it competitive with specific battery packs. The ultimate objective is to attain superior energy and power densities.
The National Science Foundation supported this work. This work was partly performed at the San Diego Nanotechnology Infrastructure (SDNI) at UC San Diego, a member of the National Nanotechnology Coordinated Infrastructure, which the National Science Foundation supports.
The study was published in the paper titled Structural Pseudocapacitors with Reinforced Interfaces to Increase Multifunctional Efficiency.
Study abstract:
Structural supercapacitors hold promise to expand the energy capacity of a system by integrating load-bearing and energy-storage functions in a multifunctional structure, resulting in weight savings and safety improvements. Here, we develop strategies based on interfacial engineering to advance multifunctional efficiency. The structural electrodes were reinforced by coating carbon-fiber weaves with a uniquely stable conjugated redox polymer and reduced graphene oxide that raised pseudocapacitive capacitance and tensile strength. The solid polymer electrolyte was tuned to a gradient configuration, where it facilitated high ionic conductivity at the electrode-electrolyte interfaces and transitioned to a composition with high mechanical strength in the bulk for load support. The gradient design enabled the multilayer structural supercapacitors to reach state-of-the-art performance matching the level of monofunctional supercapacitors. In situ electrochemical-mechanical measurements established the device durability under mechanical loads. The structural supercapacitor was made into the hull of a model boat to demonstrate its multifunctionality.
Originally published on Interesting Engineering : Original article