Accelerated life tests of complete lithium-ion battery systems for battery life statistics assessment

The paper investigates the performances of automotive lithium-ion battery systems, which are considered as one of the most promising candidates for the use on electric and hybrid vehicles. Indeed, lithium batteries show technical properties and features particularly suitable for these applications in which high energy and power densities are required. In order to investigate lithium-ion battery major technical limitations, a set of experimental testing activities has been carried on battery packs and systems, whose behaviours are expected to be significantly different from the test results on single cells. One of the most crucial challenge is the problem of the battery lifetime. Many approaches have been proposed in the relevant literature, but a lot of difficulties persist, being related to the incidence of many factors which do not allow to derive a quite general model able to describe in an exhaustive way battery performances under different operating conditions. In the paper, a method is proposed which takes into account the randomness of the battery parameters, such as design maximum specific power and operating environment, in real operating condition, with reference to lithium ion batteries designed for a small electric bus (public transport service). Based on available experimental data, the lifetime probability distribution of these batteries has been estimated by means of a Weibull model.