Determining the Effects of Non-Catastrophic Nail Puncture on the Operational Performance and Service Life of Small Soft Case Commercial Li-ion Prismatic Cells
thesisposted on 2020-12-16, 13:34 authored by Casey M JonesCasey M Jones
This work developed a novel experiment in order to determine the operational effects on a Lithium-ion battery (LIB) when a test resulting in non-catastrophic damage is performed. Accepted industry standards were used as a basis to develop a nail penetration test that would puncture a cell approximately halfway through during normal cycling at a rate of 1C, then allow the cell to continue cycling to determine how its operation was affected. The cells under test continued cycling after the punctures, showing that the experiment would be able to provide useful information on the topic. The experiment was found to be successful in simulating the operation of a cell in an abusive environment, such as those seen in electric vehicles and aerospace applications.
The results of these experiments showed that a sharp increase in temperature is observed immediately after the puncture, similar to cells that underwent tests with full penetrations. The temperatures then slowly decreased during the first few cycles after the puncture as the generated heat was dissipated through convection. The experiments also showed that it is possible for a LIB under test to continue operating for a short time after being punctured. However, the capacity and useful life of the cells were greatly reduced. The initial capacity of each cell decreased by approximately 11% after the initial impact, then continued decreasing at an accelerated rate during the ensuing cycling. The lifetime of the cells was also greatly reduced, with each cell reaching its end of life within approximately 15-75 cycles after the punctures. An analysis of the incremental capacity curves of the cells indicated that accelerated aging occurred due to both a loss of active material and a loss of lithium inventory. The information gained from the experiments gives insight into the operation of cells that experience abusive environments and will be useful in designing improved control systems, as well as promoting the development of more robust testing and safety standards for different types of cells.