Reliability Analysis of Plastic Encapsulated Coin Batteries under Harsh Environmental Conditions

A battery is an essential component of wireless sensor node (WSN) but it is typically the largest and most difficult node component for system integration and packaging. It may also be a significantly weak link for reliability, particularly in harsh environment applications. In this paper, we report on a reliability evaluation of primary coin batteries for use in plastic-encapsulated wireless sensor nodes for monitoring of steam autoclaves used for medical device sterilisation. The high temperature, high pressure steam environment is particularly harsh and places strong demands on encapsulation if batteries are to survive multiple sterilisation cycles. For the reliability evaluation, we tested three battery types of different chemistries, encapsulated with three different materials at three different thicknesses, in six different harsh environment test conditions. Using electrical monitoring and visual, scanning acoustic microscope and X-ray inspection, the reliability of the encapsulated batteries was monitored during the test cycles. There was, in general, a high failure rate, but one battery was found to survive under all test conditions. Encapsulant thickness did not have a significant influence on the reliability of this battery, a result that will allow easier integration of the battery in the final plastic-encapsulated WSN. The reliability evaluation showed that a plastic encapsulated coin battery can survive more than 200 cycles in medical autoclave and other reliability test conditions.