Complete discharge device for lithium battery

[0002] This application is a continuation-in-part of application Ser. No. 08/827,680 filed on Apr. 10, 1997, now abandoned.

[0003] The present invention relates generally to a method and apparatus to completely discharge a LiSO₂battery.

[0004] LiSO₂batteries require complete discharge prior to disposal. This is typically accomplished by a Complete Discharge Device (CDD). A CDD, typically a switch, can be actuated to complete a discharge circuit. When the battery is subject to physical abuse, self-activation, resulting in unintended battery discharge, may result if the switch need simply be depressed or slid from one position to another. One manner of preventing self-activation is to design the discharge actuator such that a special tool is required to activate the discharge function. However, such a system is cumbersome to use.

[0005] An example of such a cumbersome device is described in U.S. Pat. No. 4,965,505 which relates to the deactivation of a lithium battery by means of a switch. The discharge switch is activated by inserting an elongated object into an aperture located in the battery casing. The inserted object presses one contact against another, thereby closing the discharge circuit. While such a manner of discharging is substantially immune from self-activation, the use of a separate object to be inserted into the battery casing suffers from the drawback of being cumbersome to operate when desired.

[0006] The present invention is directed to a method and apparatus for completely discharging a LiSO₂battery.

[0007] It is an object of the present invention to provide a method and apparatus for completely discharging a LiSO₂battery which is not prone to self-activation under physical abuse conditions.

[0008] It is another object of the present invention to provide a method and apparatus for completely discharging a LiSO₂battery which does not require special tools for activation.

[0009] In order to realize the above objects, the present invention provides a method and apparatus in which a CDD actuator is used which is not prone to self-activation under physical abuse conditions. In the present invention, a switch is formed of a switch contact (e.g., a spring contact) biased toward a contact pad. When the contact and contact pad meet, the discharge circuit is activated. Under normal conditions, an elongated insulative strip is situated between the switch contact and the contact pad and extends through an aperture in the casing of the battery to form a tab. The tab allows the strip to be pulled out from the exterior of the casing. Also under normal conditions, the tab portion of the insulative strip extending through the casing is folded over and covered with a peel-off label. When it is desired to activate the CDD, the peel-off label is removed to expose the end of the strip, and the strip can be withdrawn from the casing. This then allows the contact and the contact pad to touch and activate the CDD.

[0010] The switch configured according to the present invention may be used as well to activate or inactivate other circuits, components or subsystems in addition to the complete discharge subsystem.

[0011] A more complete appreciation of this invention, and many of the attendant advantages thereof, will be readily apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings, in which like reference symbols indicate the same or similar components, wherein:

[0012] FIG. 1 shows a portion of a battery with a complete discharge device in accordance with the present invention in an unactivated condition.

[0013] FIG. 2 shows the same portion of a battery with a complete discharge device in accordance with the present invention in an activated condition.

[0014] Reference will now be made in detail to the preferred embodiment of the present invention, examples of which are illustrated in the accompanying drawings

[0015] FIG. 1 shows the complete discharge device in accordance with the present invention in an unactivated condition. Reference numeral 1 refers generally to the portion of the battery shown in FIG. 1 which includes the complete discharge device. A portion of the casing of the battery is depicted at reference numeral 2. Electronic assembly board 3, disposed within the battery casing includes contact pad 4. In order to activate discharging of the battery, contact pad 4 must touch switch contact (e.g. a spring contact) 5, thus the switch contact 5 is biased toward contact pad, 4. In the unactivated condition, an elongated insulative strip 6 is inserted into aperture 7 of the battery casing 2. The insulative strip 6, when inserted into the casing 2 separates contact pad 4 from switch contact 5, thereby preventing activation of the discharging function of the circuit. A tab portion 8 of the insulative strip 6 extends beyond the casing 2 of the battery through aperture 7, and in the unactivated condition, the tab 8 of the insulative strip 6 is bent against the exterior casing 2 of the battery. Aperture 7 and tab 8 are then covered by a peel-off label 9 which adheres to casing 2 of the battery.

[0016] FIG. 2 shows the complete discharge device of the present invention in the activated condition. In order to activate the complete discharge circuit, label 9 is peeled off the casing 2 of the battery. FIG. 2 shows the label in the peeled back state. This exposes aperture 7 and tab 8 of the insulative strip 6 extending beyond the casing. The insulative strip 6 is then removed from the battery by pulling tab 8 in the direction shown by the arrow indicated on FIG. 2. When the insulative strip 6 is removed, contact switch 5, which has been biased toward contact pad 4, touches contact pad 4. This then activates the complete discharge circuit allowing for complete discharge of the battery.

[0017] In an alternative embodiment, tab 8 is attached to label 9. Thus, when label 9 is peeled off of the battery casing 2, the tab 8 of insulative strip 6 is automatically pulled with the label, thereby eliminating the separate step of manually pulling the tab 8.

[0018] It will also be appreciated that the switching arrangement shown in FIGS. 1 and 2 can be used to activate or inactivate virtually any circuit component or subsystem, and is not limited to operation with a complete discharge device. For example, the pull tab switch can be used in conjunction with the fuel gauge (state of charge indicator or SOCI) for use in primary batteries. There is much demand for supplying primary batteries with fuel gauge to maximize the effective use of the available capacity. One of the concerns in adapting SOCI's primary batteries is that the SOCI draws current for the battery to maintain the memory of the remaining capacity even when the battery is inactive. It is common to store lithium primary batteries for more than 5 years prior to use. A significant amount of the available battery capacity would be consumed by the SOCI if stored more than a year. The pull switch according to this invention could be used to activate the SOCI only when the battery is put into use. The pull tab for the activation switch could be placed under a label over the connector which would instruct the user to remove the tab upon initial use of the battery to active the fuel gauge.

[0019] In view of the foregoing, it can be seen that the present invention provides a method and apparatus for completely discharging a LiSO₂battery which is not prone to self-activation under physical abuse conditions and which does not require special tools for activation.

[0020] It should be understood that the present invention is not limited to any particular embodiment disclosed herein. Many variations of the examples discussed above will still be within the scope and spirit of the invention, as defined by the following claims.