12 V-Class Bipolar Lithium-Ion Batteries Using Li4Ti5O12 Anode for Low-Voltage System Applications

Abstract

A combination of a Li4Ti5O12 (LTO) anode and 4 V-class cathodes has been electrochemically studied with a view to its adoption for 12 V-class bipolar batteries. Five series-connected LTO/LiMn0.85Fe0.1Mg0.05PO4 (LMFP) cells harmonized well with a useable voltage range of 12 V lead-acid batteries, which is suitable for low-voltage system applications. The LMFP cathode had excellent cycle life performance during high-temperature cycling at 60°C and over-discharge cycling tests. In the case of the LTO/Al and the LMFP/Al electrode using an Al current collector in a hybrid solid electrolyte consisting of a cubic garnet-type Li7La3Zr2O12 and a gel polymer, lithium insertion and extraction occurred smoothly without irreversible reactions in the potential range of 1 to 4.5 V vs. Li/Li+. The thin hybrid solid electrolyte with thickness of a few micrometer exhibited not only high-rate discharge but also a low self-discharge for practical use. It was demonstrated that the fabricated 12 V-class bipolar LTO/LMFP battery with a capacity of 102 mAh had the average discharge voltage of 12.5 V, the energy density of 90 Wh kg−1, and the output power density of 1500 W kg−1 for 10 s. The 12 V-class bipolar LTO/LMFP battery is expected to be suitable for low-voltage systems.