Accelerated lithium-ion battery cycle lifetime testing by condition-based reference performance tests

Lifetime testing of lithium-ion batteries is time-consuming and costly. To reduce the time-to-market, application-specific accelerated lifetime tests are conducted. The test conditions must be carefully designed and controlled, both the test environment and load profile. During the lifetime test, measurable properties of the cell, most commonly the capacity and internal resistance, are tracked by a reference performance test (RPT). The frequency of RPTs is a variable of the number of test cycles or time. Setting the wrong frequency for the RPT results in either too many RPTs or, in the worst case, too few. To mitigate this issue, a test object capacity-driven approach has been developed. This new method is described and demonstrated in this article conducting the RPTs based on the cycling capacity of the cell. The method ensured the desired numbers of RPTs during the test period at the selected intervals corresponding to steps of 1% capacity loss. When compared to the most used traditional test method, using a fixed number of 200 cycles between RPTs, the method generated 44% more cycles over the initial 100 days. • The method ensures a deterministic number of RPTs. • Provides RPTs at selected intervals during lifetime testing of Li-ion batteries. • Accelerates the ageing test in the initial stage of the test period.