Evaluation of lithium ion cells with titanate negative electrodes and iron phosphate positive electrode for start-stop applications

Start-stop systems require the battery to provide high power, endure shallow cycling, and exhibit long cycle life. The LFP/LTO (lithium iron phosphate/lithium titanate) battery is a potential candidate to meet such requirements because, at room temperature, both materials can be operated at high rate and have good stability (calendar and cycle life). In this work, we have investigated the feasibility of using LixFePO4/Li4+3yTi5O12 (0 < x < 1, 0 < y < 1) lithium ion batteries for start-stop systems. We evaluate both the rate and temperature dependence of LFP/LTO cells subjected to galvanostatic charge/discharge cycling. Excellent rate performance was observed at temperatures above or at ambient. However, at low temperatures, significant resistance is observed, and this must be addressed for the LFP/LTO system to be viable. In addition, we investigate the SOC dependence of equivalent circuit parameters using triangular current and voltage excitation method to facilitate the implementation of circuit-based control algorithms for vehicle applications. Parameter values are nearly constant over the broad voltage-plateau region of the substantially two-phase behavior of both the LFP and LTO materials.