High Impedance Battery Research

What is a high impedance battery?

A High Impedance Battery is an electrochemical cell with a high internal resistance. It produces voltage but very little current.                

Their life exceeds that of low internal resistance cells by factors of ten, since the cell dipole is maintained for much longer by the low current drain.

Field of Application

The class of High Impedance Batteries are ideally suited for driving High Impedance Loads that require only very small current, such as Electrostatic Motors.

In the days when Vacuum Tubes or Valves were commonplace, the "C" battery used to apply a potential to the grid of the electron tube would last for as long as its shelf life since it was only applying a voltage to the grid - no current flowed from the battery.

The combination of High Impedance Batteries with Electrostatic Motors offers the possibility of greatly increased efficiency for Electric Vehicle applications. The energy density of conventional cells is now becoming high enough to offer enough range for EVs to be psychologically competitive with Internal Combustion Engine (ICE) vehicles, notwithstanding the average trip length of 20 miles that motor cars are generally used for. However, the High Impedance Battery and Electrostatic Motor combination could offer still greater efficiencies.

The Sodium Nickel Chloride battery in production today has an energy density of about 120Wh/kg, four times that of lead acid.  Lithium Ion batteries are also currently able to provide about 120 Wh per kg weight in real world conditions, though some development systems can go up to 200Wh/kg; Zinc Air has demonstrated about 220 Wh/kg and the Lithium Sulphur system in development may hold 400Wh per kg (but with restricted cycle life and volumetric density not significantly better than LiIon).

Petrol has an energy density of about 13kWh per kg but 85% of the energy in petrol is wasted as heat - only 15% is converted into useful work in an Internal Combustion Engine. A battery with 2000Wh per kg energy density would therefore more or less equal the effective energy density of petrol, taking into account the fact that the Electric Motor - Battery system is also much more efficient than the Petrol - ICE system; 90% conversion efficiency of electrical power input into mechanical output is normal in an AC or DC electric motor.

There is no electrochemical battery on the market today that can reach an energy density of 2000Wh/kg in the foreseeable future. Only the Li Air or Li Water Fuel Cell has reached 1100Wh/kg and has a theoretical specific energy of 11,000 Wh/kg. This is a very interesting future candidate for very high energy density batteries.

The Finnish company Europositron claim to have developed a rechargeable Aluminium Air battery with a specific energy of 1300Wh/kg. This is also a very interesting and potentially highly important development.

Electric cars today average between 4 and 8 miles range per kWh of stored electricity.  At teh upper end, a mass market appeal electric car would therefore ideally have about 100kWh of battery storage.  This would equate to 100kg of Lithium Air fuel cell storage or only 80kg of AlAir - outstanding figures. But with current technology LiIon batteries, with a real world specific energy of 150Wh/kg at best, the weight would be over 650kg - prohibitively heavy and expensive.

However, if we were to take a High Impedance Battery - Electrostatic Motor approach, an even more efficient electrical motive power system could be produced that could equal and surpass the energy density of the petrol powered automobile.

Technical Explanation

An electromagnetic motor requires a rotating magnetic field to drive the armature. This is produced by energising and de-energising in sequence the electromagnets of the stator. Even though little energy is lost when a current is applied to a solenoid - the energy applied is stored in the magnetic field of the coil - that energy is lost when the voltage is released and the back EMF is produced. Certain EM Motor concepts capture that back EMF and divert it to re-charge the battery, which is certainly another approach to ultra efficient EM Motors that would greatly extend the range and efficiency of vehicles powered by conventional batteries or cells.

An alternative approach is to use voltage only motors that require very little current - Electrostatic Motors.

Electrostatic Motors can easily exceed the power per unit weight capabilities of Electromagnetic Motors but up to now have taken up more volume than the equivalent EM motor.  However, the higher the electrode density the smaller the volume and the higher the power to weight ratio of an ES motor.  Research at the University of Tokyo into thin film pulsed ES motors that will operate on less than 1000 Volts could offer significant reduction in the size of ES Motors.  Very high mechanical power outputs are also being achieved.

High Impedance Batteries that Meridian International are researching include Cu - Zn, Cu - Al and CuO - Al cells.

We are also researching improvements for a next generation of ES Motors using optimised dielectrics, electrets, differential electrode metals and new geometries.

Atmospheric Motors Remediation

 
 

Copyright 2005 Meridian International Research
Last updated 22/09/05