Tech Insights

Novel Energy Storage Capacitors Set to Replace Batteries

May 30, 2024 by Jake Hertz

Researchers have identified a material structure to enhance the energy storage capacity of capacitors. 

Capacitors are gaining attention as energy storage devices because they have higher charge and discharge rates than batteries. However, they face energy density and storage capacity challenges, limiting their effectiveness for long-term energy storage. Capacitors also suffer from self-discharge and voltage limitations, which affect their reliability and performance over time.  

Researchers in St. Louis, Missouri, may have a solution to improve capacitors as energy storage devices. They have identified a new material structure that improves capacitors’ charge-discharge cycle efficiency and energy storage capability.

 

Capacitors

Capacitors. Image used courtesy of Wikimedia Commons

 

Batteries vs Capacitors

Internally, a battery comprises three primary components: two electrodes and an electrolyte. The electrodes must conduct ions without allowing electrons to pass, and the electrolyte forces electrons to exit the battery via the terminals when connected to a circuit. By nature, power is stored in batteries as chemical potential. 

Capacitors typically have two conductive plates separated by a non-conductive material called a dielectric. When a voltage is applied, electrons build up on one plate, creating a negative charge, while the other plate becomes positively charged. This charge separation creates an electric field, storing energy in the capacitor. Capacitors with larger surface areas can store more charge, and a more insulated gap allows for a higher charge capacity.

 

Capacitor structure

Capacitor structure. Image used courtesy of Wikimedia Commons

 

While batteries and capacitors are both energy storage devices, they differ in some key aspects. A capacitor utilizes an electric field to store its potential energy, while a battery stores its energy in chemical form. Battery technology offers higher energy densities, allowing them to store more energy per unit weight than capacitors. However, batteries may discharge more slowly due to chemical reaction latencies. In contrast, capacitors can discharge and charge more quickly because they store energy directly on their plates, which is related to their conduction capabilities. 

Researchers are working to enhance battery charging and discharging times to meet the demand for fast, portable power while also aiming to increase capacitor storage capacity.

 

Beyond Batteries

A research team at Washington University in St. Louis recently discovered a material structure that could improve capacitors’ efficiency, potentially rendering batteries obsolete. The study, published in Science, demonstrated a heterostructure that reduced energy loss, allowing capacitors to store more energy and charge rapidly without sacrificing durability.

Ferroelectric materials within capacitors offer high maximum polarization, which is advantageous for ultra-fast charging and discharging. However, this property can limit the conductor’s energy storage effectiveness or relaxation time. Relaxation time refers to how long the capacitor's charge takes to decrease to a certain percentage of its initial value after charging or discharging. It is determined by capacitance and resistance, indicating how quickly the capacitor returns to equilibrium after a voltage change. The precise control over relaxation time holds promise for various applications and could accelerate the development of highly efficient energy storage systems.

The research team presented a method to regulate relaxation time by employing two-dimensional (2D) materials while minimizing energy loss using 2D/3D/2D heterostructures and maintaining the crystallinity of ferroelectric 3D materials. By layering 2D and 3D materials in atomically thin layers, employing both chemical and nonchemical bonds between each layer, a thin 3D core is inserted between two outer 2D layers. This creates a stack of only 30 nanometers thick, approximately one-tenth the size of an average virus particle. The researchers used two-layer molybdenum disulfide and barium titanate for the study. 

This approach attained an energy density of 191.7 joules per cubic centimeter with an efficiency exceeding 90%.

 

Unlocking the Future Capacitor

The research could significantly impact power storage by merging the benefits of capacitors and batteries into one device. This development is particularly significant for electric vehicles, where capacitors have the potential to provide rapid energy bursts without sacrificing performance.