The Importance of Testing and Designing Lithium-Ion Batteries in the Relevant Environment

Lithium-ion batteries have the highest energy density and cycle life of the rechargeable battery chemistries in the commercial battery market today.  However, associated with that high energy density is its tendency to go into thermal runaway when the battery is not designed or used appropriately.  Although the size of the lithium-ion batteries in various applications are growing in energy and power, the nature of tests carried out to characterize their safety has not grown to adequately understand the hazards associated with the battery designs.  Typical hazards associated with these batteries are overcharge, external and internal short circuites and high temperatures.  Thermal runaway can occur in these batteries in many ways including the failure of internal cell protective devices.  One needs to characterize not only a cell design but also the appropriate module and battery design especially if the cell level controls are used as one of the first two levels of control. The thermal dissipation characteristics and the propensity of any cell going into thermal runaway to propagate to other cells should also be considered for faults that are not fully understood at the battery level for the environment it is to be used in.  Stringent certification and qualification tests of the battery design in the relevant environment with post-test destructive and non-destructive analysis will help in defining the safety as well as provide insight on the robustness of the safety controls.  This paper will discuss the various aspects of the li-ion battery design that needs to be characterized and provide some insight into recommended design solutions.