Isotopic semiconductor batteries

Details Isotopic semiconductor batteries Isotopic semiconductor batteries

1998-04-06

2001-05-29

Brouillette, Gabrielle (Department: 1745)

Chemistry: electrical current producing apparatus, product, and

Radio active material containing

C310S302000, C310S303000

Reexamination Certificate

active

06238812

ABSTRACT:

TECHNICAL FIELD OF THE INVENTION
This invention relates in general to batteries and relates more particularly to batteries that are powered by direct conversion of the energy of radioactive decay processes into stored electrical energy without going through a thermal cycle. Because the decay lifetimes of these nuclear decay processes can be thousands of years, these batteries will exhibit comparable useful lifetimes.
BACKGROUND ART
A conventional battery, such as a conventional chemical car battery, contains: a first set of electrodes of a first material; a second set of electrodes of a second material; and an acidic fluid in which these two electrodes are immersed to produce an electrical path between these two electrodes. These two sets of electrodes are selected to have significantly different electrochemical work functions W
1
and W
2
, so that, when an external current path is provided between these two electrodes, a current is produced from the first electrode, through this external conductive path to the second electrode. This type of battery provides a peak voltage that is substantially equal to the difference between the electrochemical potentials of these two electrodes. The lifetime of conventional batteries is relatively short, because chemical energies are relatively small. Therefore, cars include generators that are powered by means of a first fan belt that is driven by the car's gasoline motor. These generators are connected to the battery by electrical leads that maintain the battery's stored chemical energy.
Many applications require batteries that have extremely long lifetimes. For example, space probes that will travel for many years before reaching their destinations, need to utilize batteries that have extremely long lifetimes. Similarly, many devices, such as computers, are connected to power sources that are designed to protect that device from power spikes in power lines to which these devices are connected. These devices also typically include batteries that contain at least enough stored energy that the computer has time to shut down in a manner that saves unstored data that has been keyed into this computer. It would be advantageous for these devices to have enough stored energy to power the computer for a day or even a few days which should be sufficiently long for the power company to correct its power distribution problem. These batteries would also be useful in smoke detectors, so that lives are not put at risk because the smoke detector's batteries lost their stored electrochemical energy. It is of crucial importance to have extremely long life batteries in space probes and any other application in which it is difficult or impossible to replace the batteries. However, even in applications in which it is merely inconvenient to have a battery go dead, it is advantageous to have long-life batteries, because such batteries need be replaced only at very long intervals.
FIG. 1
illustrates a battery
10
that is taught in U.S. Pat. No. 5,087,533 by Paul M. Brown, entitled
Contact Potential Difference Celle
that was issued on Feb. 11, 1992. Battery
10
contains: (1) a first electrode
11
that has a first work function W
1
; (2) a second electrode
12
that has a second work function W
2
that is larger than W
1
, and (3) two or more nonconductive spacers
13
that keep electrodes
11
and
12
at a fixed spacing to produce a cavity
14
in which a gas or solid is ionized by a flux of radiation that has sufficient energy to ionize molecules or atoms in this radioactive material. This radiation flux can be provided by a variety of sources, such as a nuclear reactor, an external block of radioactive material or radioactive material within this battery. This radioactive material can be provided in several forms, such as: a gas, a liquid, a gel or a solid.
Because the work function of electrode
12
is larger than the work function of electrode
11
, when one or more electric conductors
15
are connected between electrode
11
and electrode
12
, a negative charge is produced on electrode
11
and an equal positive charge is produced on electrode
12
. The resulting electropotential difference between these two electrodes is equal to the difference between the work functions of these two electrodes. This electropotential difference produces an electric field {right arrow over (E)} that extends from electrode
12
to electrode
11
. Free electrons and negative ions in cavity
14
are drawn toward the more lectropositive electrode (i.e., electrode
11
) and the positive ions are drawn toward the more lectronegative electrode (i.e., electrode
12
). The total current I between electrodes
11
and
12
is the sum of the electron current I
e
and the total ion currents I
i
.
This current flux experiences negligible resistance within the battery, because the density of ions and free electrons within cavity
14
is so low, that there is negligible scattering among these electrons and free ions. The small number of collisions between the electrons, ions and neutral particles in cavity
14
produces an extremely low level of excited states that can radiate away small amounts of energy. Therefore, resistive losses are extremely small compared to resistive losses in conventional batteries. Thus, these batteries not only exhibit extremely long half-lives (e.g., 458 years for Americium-241), they also exhibit extremely low heat dissipation rates. When a radioactive gas is supplied to cavity
14
, the resulting positive and negative ions injected into the cavity by radioactive decays have sufficient energy to ionize a significant fraction of the gas ions within this cavity. Because the radioactive decay energies are typically on the order of millions of electron volts, the energy needed to ionize an atom that is impacted by a radioactive decay product is only a few electron volts (on the order of 32 eV), each radioactive ion can ionize on the order of a million gas molecules. This battery therefore exhibits an incredibly long lifetime, compared to electrochemical batteries.
Unfortunately, the metallic electrodes in this prior art battery are bulky, which significantly reduces this battery's efficiency and increases its weight. In addition, its design is not amenable to the integrated circuit processes that enable the manufacture of circuits to be produced in small size and/or to be produced inexpensively by these integrated circuit processes.
FIG. 2
illustrates a prior art battery
20
that consists of a series stack of N (=7) battery cells
10
of the type presented in FIG.
1
. Battery
20
therefore provides a potential difference of N·(W
1
−W
2
) across a resistor
21
of resistance R. Each of battery cells
10
exhibits an inherent resistance r, so the total resistance of the closed conductive path from the top of layer
11
, through layers
12
and
13
back to the top of layer
11
is N·r+R. Therefore, the current I in this closed circuit is equal to N·(W
1
−W
2
)/(N·r+R).
U.S. Pat. No. 5,246,505 entitled “System and Method To Improve the Power Output and Longevity of a Radioisotope Thermoelectric Generator” issued to Alfred Mowery, Jr. on Sep. 21, 1993 discloses an electrical power source that uses waste heat that is produced by radioactive decays of a highly radioactive material, such as plutonium. The energy in these nuclear decay products is converted into heat that is then converted into electrical energy by conventional methods, such as thermocouples that are distributed around the plutonium source. Unfortunately, the amount of heat involved is so large that the expensive process of helium outgassing is used to cool the radioactive source so that the thermal degradation does not severely degrade apparatus lifetime. Unfortunately, this thermoelectric generator exhibits the disadvantages of the conventional thermoelectric generator designs—namely: very low energy conversion efficiency, expensive manufacture, a large, heavy structure and substantial shielding to prevent health risks caused by the use of a

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