All-electronic charge storage devices with large energy density and small leak currents
Abstract
Summary: During the past five years, nanotechnology has begun to enhance the density of electrical energy storage. Electrochemical batteries, electrostatic capacitors and hybrid devices, such as electrical double-layer capacitors which make use of both electrochemical and electrostatic storage principles have recently been improved by incorporating nano-scale features. The proposed all-electronic charge storage device is a stack of nanocapacitors. Most rechargeable chemical batteries employ ionic reactions, because these reactions can be easily reversed. This limits the energy density to about 1GJ/m3. In contrast, all-electronic rechargeable charge storage devices can be made of materials with covalent bonds, such as boron nitrate with an energy density of 1600GJ/m3 in the bonds. Therefore the energy density in allelectronic charge storage devices can be several orders of magnitude larger than in chemical batteries. The voltage of Faradic systems is limited by the electrochemical potentials which are typical around 1 Volt. However, energy efficient distribution systems require much larger voltages. 100 batteries in series can deliver hundreds of volts, but have severe safety problems, such as cascading failures and thermal run-away. All-electronic charge storage devices can store and deliver charges at a much higher voltage. For instance a 600 nm SO2 nanocapacitor has a dielectric strength of 200Volt. The self-discharge time of a charged capacitor without load is independent of the gaps size, whereas the maximum charge density is inversely proportional to the gap size. This means that stack of nanocapacitors can store much more charge than macroscopic capacitors with the same volume. We propose to use this insight to engineer all-electronic charge storage devices with a record charge density. The leak current in vacuum nanocapacitors is due to field emission of electrons on the cathode and a ballistic motion of the electrons towards the anode. In contrast, in 3 electrode capacitor devices, where a thin anode is sandwiched between two cathodes, there is quantized space charge in the vacuum gaps. This quantized space charge screens the electric field and suppresses the field emission current, due to Coulomb blockade. We propose to design multielectrode charge storage systems with a record low leak current. In all-electronic systems, no atoms are moving, only electrons. Electrons are 1000 times less massive and move almost with the speed of light in conductors (Fermi velocity). In contrast, in Faradic systems the motion of the charged particles is limited by diffusion, which is about 10 orders of magnitude slower. Therefore the power density of all-electronic charge storage systems is very large. We will design and fabricate all-electronic charge storage devices with a large, potentially a record power density. Some nanocapacitors regain their dielectric strength within a few minutes after break down. We will study self-healing nanocapacitors. The most important competing technology are chemical micro batteries, because they should have a much higher power density and be more reliable than macroscopic chemical batteries. However there is an old, unsolved problem: The energy storage capacity decreases rapidly within a few charge/discharge cycles, in particular for rapid charging/discharging cycles. We believe the problem is associated with a highly nonlinear interaction between electric fields and a complex surface chemistry. We will do exploratory work in controlling non-Faradic reactions in the vicinity of charged surfaces.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Aug 12, 2016
- Source ID
- N000141512397
Entities
People
- Alfred Hubler
Organizations
- Office of Naval Research
- United States Navy
- University of Illinois Urbana–Champaign