Application to lithium battery electrolyte of lithium chelate compound with boron

Abstract

The electrolytic conductivities and charge–discharge characteristics of lithium electrode are examined in propylene carbonate (PC)- and ethylene carbonate (EC) tetrahydrofurans, such as 2-methyltetrahydrofuran (2-MeTHF) and 2,5-dimethyltetrahydrofuran (2,5-DMeTHF), binary solvent electrolytes containing lithium bis[1,2-benzenediolato(2-)- O, O′]borate (LBBB), lithium bis[2,3-naphthalenediolato(2-)- O, O′]borate (LBNB), lithium bis[2,2′-biphenyldiolato(2-)- O, O′]borate (LBBPB) and lithium bis[salicylato(2-)]borate (LBSB). The order of specific conductivities in PC- and EC-based equimolar binary solutions containing these organoborates is LBBB≥LBNB>LBSB>LBBPB. The conductivity in LBNB electrolyte with higher viscosity than that in LBSB electrolyte becomes high. The PC–2-MeTHF and PC–2,5-DMeTHF equimolar binary solutions containing LBSB and a mixed electrolyte (LBBPB+LiPF 6) show very high cycling efficiencies more than 90% at a higher range of cycle number. The EC–THF and EC–2-MeTHF equimolar binary solutions are moderate electrolytes with about 80% cycling efficiencies. It is found by using scanning electron microscope (SEM) that the films formed on the electrode in PC–2-MeTHF and PC–2,5-DMeTHF electrolytes with higher cycling efficiencies have a homogeneous surface with uniform grain size.