PRIMARY HIGH ENERGY DENSITY BALANCED CELL WITH SAFETY CIRCUIT

Abstract

A primary electrochemical cell having a capacity in excess of 0.5 AHr and a high energy density anode comprised of a metal selected from lithium, sodium, potassium, calcium and manganese and a cathode active material, wherein the discharge capacity of the anode is at least substantially equal to or in excess of the discharge capacity of the cathode active material, and wherein said cell further comprises a voltage monitor and cell circuit cut-off whereby when the voltage monitor senses a discharge voltage of about 1.6 or lower, said circuit cut-off are actuated to cut off the cell circuit to thereby prevent hazardous conditions of cell reversal or anode metal plating.

Description

These and other objects, features and advantages of the present invention will become more evident from the following discussion and drawings in which:

SHORT DESCRIPTION OF THE DRAWINGS

FIG. 1 is a depiction of a high energy density electrochemical cell with partial cut-out section and with a balanced stoichiometric anode and cathode capacity arranged in series with other cells and with a voltage monitor and cell circuit shutoff member.

DETAILED DESCRIPTION OF THE INVENTION

Generally the present invention comprises a primary electrochemical cell having a lithium metal anode or similar high energy density anode including sodium, potassium, calcium, magnesium and the like. Typical cathode active materials in such primary cells include sulfur dioxide, thionyl chloride and various metal oxides such as manganese dioxide, cobalt oxide, nickel oxide, iron oxide and the like. In accordance with the present invention the electrodes in the cells are essentially electrochemically balanced to attain maximum capacity from the high energy density electrochemical system. Cells with an overall capacity of at least about 0.5 AHr, can present a safety problem with cell reversal or anode plating in a primary cell. A typical D size cell with a lithium anode, sulfur dioxide depolarizing cathode material and a carbon cathode has capacity of about 8-9 AHr while the slightly more expensive C cell Li/MnO₂ has a capacity of 11-12 AHr with both of such cells being dischargeable at moderate to high discharge rates.

In order to ensure that such anode limited or stoichiometric balanced cells of the present invention are not liable to detrimental cell reversal and the like, the cells are each provided with voltage monitoring means. The voltage monitoring means is electrically placed in the cell discharge circuit and is adapted to trigger cell shut down when the individual cell voltage reaches a dangerous voltage at which untoward conditions will occur. For high energy density cells this is generally about 1.6 volts or lower. The 1.6 volts for the high energy density cells is the point of no return for the reversal/plating condition. The cell shut down means include solenoids which are triggered to mechanically break the cell/battery discharge circuit. Alternatively, solid state power transistors can be used to electrically effect the cut off at the requisite voltage by high resistance. Similar means of cell discharge cutoff are possible and readily available.

In a preferred embodiment the cells are mounted on a flexible circuit board containing the circuitry of a voltage monitor and triggering means for cell/battery-shut off.

DETAILED DESCRIPTION OF THE DRAWINGS

With respect to the drawings, FIG. 1 depicts a typical D size high energy density cell 10 with a lithium anode 1 and a manganese dioxide cathode 2 present in essentially stoichiometric balanced ratio. The cell 10 is shown in linked series circuit 30 with cells 11 and 12 and an electrical device 20 powered thereby. Cell 10 is provided with voltage detector 13 (cells 11 and 12 are similarly provided but not shown). Voltage detector 13 is set with a cutoff voltage monitor of about 1.6 volts. When the cell voltage drops to this level, switch 14 opens and the cell circuit 30 is opened to stop any cell reversal or lithium plating. It is not however sufficient to provide only one cell with the monitor since it may be another cell which undergoes the reversal and voltage drop. The monitor is accordingly preferably attached to all the cells in a battery.

It is understood that the above description and drawings are merely exemplary of the present invention and that changes may be made in cell structure and components as well as the monitoring device and means for cell circuit cut-off without departing from the scope of the present invention as defined in the following claims.

Claims

1) A primary electrochemical cell having a capacity in excess of 0.5 AHr and a high energy density anode comprised of a metal selected from lithium, sodium, potassium, calcium and manganese and a cathode active material, wherein the discharge capacity of the anode is at least substantially equal to or in excess of the discharge capacity of the cathode active material, and wherein said cell further comprises voltage monitor means and cell circuit cut-off means whereby when the voltage monitor means senses a discharge voltage of about 1.6 or lower, said circuit cut-off means are actuated to cut off the cell circuit to thereby prevent hazardous conditions of cell reversal or anode metal plating.