Abstract:
The invention is a thermal battery system. In detail, the battery system includes housing. A plurality of battery cells containing an electrolyte that is in a non-operating condition at ambient temperatures and in an operating at condition at elevated temperatures is mounted within the housing. A wire heating assembly is mounted within the housing for heating the electrolyte to operating temperatures, upon the application of electric power thereto. Preferably, the heating assembly comprises a plurality of heating coils wound about the battery cells.

Description:
RELATED APPLICATIONS  
       [0001]    This application is a continuation-in-part of co-pending provisional patent application Serial No. 60/227,743 “Electrically Heated Thermal Battery” filed Aug. 24, 2000. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The invention relates to the field of batteries and, in particular, to thermal batteries and systems for heating such batteries to operating temperatures.  
           [0004]    2. Description of Related Art  
           [0005]    Thermal batteries are noted for their extremely high discharge rate and power delivered for short periods of time and generally has a very long storage life. A typical prior art thermal battery comprises a plurality of cells having metallic positive electrode and a metallic negative electrode spaced apart with an inactive electrolyte that becomes electrically active when heated. A combustible material is disposed between the cells and in contact therewith for supplying heat to the electrolyte, which is actuated by an explosive squib. The combustible material is typically a mixture of a finely divided metal oxide and a finely divided metal such that it will exothermically react to form an electrically conductive oxide. Thus this material contributes greatly to the weight of the battery. Upon ignition, the combustible material heats the electrolyte to a temperature wherein it melts.  
           [0006]    At this point, the battery will produce electrical energy, unfortunately for only a short period. Thus they have general application as a back-up power supply. In addition, they have application in non-emergency systems. On launch vehicles and spacecraft there is often a need for large amounts of electrical energy for short periods. The weight of conventional batteries would be prohibitive. However, thermal batteries weighing as low as a few pounds provide more than adequate performance. An extreme example is that two fifty pound thermal batteries providing 270 volts and 450 amperes for three minutes can replace 2500 pounds of conventional batteries. A typical thermal battery is disclosed in U.S. Pat. No. 4,041,217 “Thermal Battery With Metal Oxide Heating Composition” By W. H. Collins.  
           [0007]    As previously mentioned, such thermal batteries are short lived. For once the heat generating chemicals are exhausted, the battery begins to cool down, and over a rather short period of time, the electrolyte becomes inactive while still having stored electrical power. However, many such batteries loose their charge, before the electrolyte becomes inactive. There have been attempts to build non-pyrotechnic heated thermal batteries; however, these used external heating enclosures to heat the entire battery assembly. Such systems would be extremely heavy and impractical for use on launch vehicles or spacecraft.  
           [0008]    Of course, conventional battery heating systems are old in the art. For example U.S. Pat. No. 3,623,916 “Storage Battery With Heater” by T. Toyooka, et al. discloses a battery design wherein a wire heating element is incorporated into the battery casing and connected the terminals thereof in order to maintain the electrolyte at optimum temperature. Also of interest is U.S. Pat. No. 5,158,841 “High-Temperature Storage Battery” by S. Mennicke, et al., which discloses a cooling system for a battery disposed about the cells for conducting heat therefrom during periods of operation. A wire heating grid is provided at the bottom of the cells for maintaining the cells at operation temperature during non-operating periods. However, the problem with most thermal batteries is maintaining them at operating temperatures, and cooling is not an issue. The use of a heating grid at one end of the battery cells is most inefficient.  
           [0009]    Thus, it is a primary object of the invention to provide a thermal battery that can be continuously maintained at operating temperature.  
           [0010]    It is another primary object of the invention to provide a light weight thermal battery.  
           [0011]    It is a further object of the invention to provide a thermal battery that can be recharged.  
         SUMMARY OF THE INVENTION  
         [0012]    The invention is a thermal battery system. In general, the battery system includes housing. Mounted with the housing are a plurality of battery cells containing an electrolyte that is in a non-operating condition (non-conductive) at ambient temperatures and in an operating condition (the electrolyte is conductive) at elevated temperatures. When heated, the electrolyte remains semi-ridged, but does tend to flow over time. A wire heating assembly is mounted about the plurality of battery cells for heating the electrolyte to operating temperatures, upon the application of electric power thereto. Preferably, the heating assembly comprises heating coils wound about the battery cells.  
           [0013]    To provide efficient heating of the battery cells, the housing contains a first insulation layer mounted about the battery cells. A second ridged layer of insulation, preferably made of Mica, is mounted about the first layer of insulation extending about the battery cells with the wire heating element assembly mounted about thereabout. This ridged layer of insulation prevents any of the electrolytes from reaching and damaging the heating wires. Preferably, the wire heating assembly is made of nickel-chrome wire. A third layer of insulation is mounted about the wire assembly. If desired a charging system can be coupled across the positive and negative poles of the battery cells for re-charging the cells.  
           [0014]    In a second preferred embodiment the thermal battery system includes a first housing with the electrical energy supplying assembly for supplying electrical power when heated to operating temperatures mounted within the first housing. A wire heating assembly is mounted about the first housing for heating the electrical energy supply assembly to operating temperatures. A second housing is mounted about the fist housing and the wire heating assembly. A first insulation layer is mounted about at least a portion of the electrical energy supplying assembly within the first housing and a second insulation layer is mounted between the first and second housings about the wire heating element assembly.  
           [0015]    The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages thereof, will be better understood from the following description in connection with the accompanying drawings in which the presently preferred embodiments of the invention are illustrated by way of examples. It is to be expressly understood, however, that the drawings are for purposes of illustration and description only and are not intended as a definition of the limits of the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    [0016]FIG. 1 is a cross-sectional of the thermal battery.  
         [0017]    [0017]FIG. 2 is a cross-sectional view of FIG. 1 taken along the line  2 - 2 .  
         [0018]    [0018]FIG. 3 is a cross-sectional view of battery cell.  
         [0019]    [0019]FIG. 4 is a cross-sectional view of a second embodiment of the thermal battery. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0020]    Illustrated in FIG. 1 is a thermal battery assembly, generally indicated by numeral  10 , comprising a hermetically sealed circular container  11  having a side wall  12  and top and bottom covers  13 A and  13 B. A battery  14  made up of a plurality of cells  14 A, B, C, D, E, F, G, H. Referring to FIG. 2 each cell, for example cells  14 B and  14 C, comprise a cathode  16 , anode  18 , solid electrolyte  20  and conductive spacers  22 . A typical cathode  16  will be made of a material such as iron pyrite (iron disulfide, FeS 2 ), a typical anode  18  will be made from a material such as a lithium -silicon alloy, the spacers  22  will be made from stainless steel alloy, while the electrolyte  20  is made of a mixture of alkali halide salts. Of course, there are numerous other combinations of materials. The actual chemical makeup of the cells is not a critical to the invention; thus the cell structure need not be discussed in further detail.  
         [0021]    Referring back to FIG. 1, the cells are connected in series by the conductive spacers  22 . Non conductive spacers  23 A and  23 B further insulate the battery cells  14 A- 14 H from the top and bottom covers  13 A and  13 B of the housing  11 . Lead wires  24  and  26  connect the cells  14 A- 14 H to connectors  27  and  28  mounted in the in the top and bottom covers  13 A and  13 B, respectively, of the housing  11 . These lead wired  24  and  26  also extend through holes (not shown) in the spacers  23 A and  23 B and top and bottom covers  36 A and  36 B, respectively, of the container  32 .  
         [0022]    The plurality of battery cells  14 A- 4 H are placed under compression and wrapped with an inner flexible high temperature insulation layer  30 . A suitable high temperature insulation material is Fiberflax® manufactured by Unifrax Corporation, Niagara Falls, N.Y. A ridged container  32 , having a side wall  34  and top and bottom walls  36 A and  36 B, is positioned about the wrapped stack  14 A- 14 H made of quartz like material such as mica. Heating element  40 , preferably made of nichrome wire, is wrapped about the side wall  34  of the container  32  and is connected to terminals  42 A and  42 B in the top and bottom covers  13 A and  13 B, respectively, of the container  11 . Additional flexible high temperature insulation layers  44  are wrapped about the heating element  40 . Electrical lead  46  and  48  connect to terminals  50  and  52 , respectively, on the top and bottom covers  13 A and  13 B. Finally, battery-charging circuit  56  can be coupled to the terminals  27  and  28  for charging the battery assembly. In addition, a heater control system  57  is provided to control the heating level of the battery  14   
         [0023]    Thus electrical power source (not shown) is coupled to connectors  42 A and  42 B, the electrolyte is heated until it becomes active. The battery is then active and can supply very large amounts of power for a short period of time. After it is discharged, but still at high temperature, battery charger  56  can recharge it. Even after the battery has been allowed to cool to a point that the electrolyte is non-conductive, the heating wires can be activated and the charger  56  used to recharge. Thus not only is thermal battery reusable, but the elimination of the pyrotechnics used for heating in the prior art designs is eliminated.  
         [0024]    [0024]FIG. 4 presents a second embodiment of the invention. The thermal battery assembly, generally designed by numeral  60 , includes a top plate  62  having a circular protrusion or boss  64 . A circular metal cup  66  having a side wall  68  and bottom wall  70  is joined by its open end  72  to the boss  64 . The cup  66  maybe joined to the boss  64  by any number of conventional joining techniques, such as by welding. Mounted generally within the center of the cup  66  is the previously mentioned battery  14  surrounded by insulation  76 . Lead wires  78  and  80  connect the battery  14  to an external circuit  81  via connectors  82  and  84 , respectively, mounted in the in the top plate  62 . The external circuit  81  is coupled to a battery charging circuit  86 .  
         [0025]    A heating element  90 , preferably made of nichrome wire, is wrapped about the side wall  68  of the cup  66 . Lead wires  96  and  98  connect to external circuit assembly  100  via connectors  102  and  104 , respectively, mounted in the top plate  62 . The circuit assembly  100  includes a power supply assembly  106 . A second cup shaped member  108  is mounted about the heating element  90  and cup  62  and is also joined to the top plate  62 . The space between the two cups  62  and  108  is also filed with insulation  110 , between the housing  66  and heating element  90  and between the heating element and second cup shaped member  108 . Operation is similar to a normal thermal battery.  
         [0026]    The advantage of this second battery assembly  60  is that the use of a metal cup  66  insures that none of the heated electrolyte can reach the heating wire element  90  causing damage thereto. In addition, the design has far more structural integrity.  
         [0027]    While the invention has been described with reference to particular embodiments, it should be understood that the embodiments are merely illustrative, as there are numerous variations and modifications, which may be made by those skilled in the art. Thus, the invention is to be construed as being limited only by the spirit and scope of the appended claims.  
         [0028]    Industrial Applicability  
         [0029]    The invention has applicability to the battery manufacturing industry.