Abstract
A long-term operation test of a specially developed electric bus has been performed as part of a project organized by the Japanese Ministry of the Environment. The following battery-related information was obtained. (1) The bus was driven for 48,714 km over 1,872 days and charged 4,958 times. As a result, the capacity of the on-board lithium-ion batteries (LIB) fell by approximately 25% and the internal resistance increased by approximately 50%. An evaluation method was proposed and adopted that estimated the capacity and internal resistance from easily obtainable terminal voltage and current data without removing the battery and performing detailed measurements. (2) Various measures were proposed and adopted to extend the battery lifetime. These included rotating the batteries between installation positions under different temperature environments, and adopting a battery-friendly seasonally variable charging rate method that reduces the charging power in seasons with lower power consumption. Simulations predicted that these measures have the potential to increase capacity retention by several % over 10 years from battery manufacture.
