Standardizing mechanical tests on li-ion batteries to develop a useful cell-level model under extreme mechanical loads

Mechanical characterization of Li-ion battery cells is becoming increasingly important as the community becomes more aware that the underlying mechanisms of battery failure and degradation involve the complex interplay between electrochemistry and mechanics. Various types of mechanical tests have been developed, and how the tests are performed varies among individual research groups. Till today, there are no widely accepted standards acting as guidelines for battery mechanical engineers. This paper is motivated by our deep concern that nowadays various mechanical models are being developed, some of which were based on a limited number of tests but have led to ambitious conclusions about the modeling effectiveness. Here, through our test data and simulation results, we reveal that many existing types of cell-level mechanical tests can only result in a narrow stress state and thus could not be used to validate one another. This paper will also perform a careful examination of each individual test and provide the users with our recommendations on the choice of mechanical tests, the role of each test, and how to perform them. We hope that this paper can initiate a wide discussion among the battery modeling community leading to a standardized testing procedure soon.