LiBF₄-Based Concentrated Electrolyte Solutions for Suppression of Electrolyte Decomposition and Rapid Lithium-Ion Transfer at LiNi_0.5Mn_1.5O₄/Electrolyte Interface

Charge and discharge properties of spinel LiNi 0.5 Mn 1.5 O 4 positive electrodes were investigated using concentrated LiBF 4 /propylene carbonate (PC) electrolyte solutions in the range of 0.833 (ca. 1 mol dm −3 ) to 7.25 (nearly saturated) mol kg −1 . The irreversible decomposition of electrolyte solution was effectively suppressed with an increase in concentration. In addition, the polarization in charge/discharge reactions remained small in the nearly saturated 7.25 mol kg −1 LiBF 4 /PC even though the viscosity was very high and the ionic conductivity was low. The rate capability was higher than that obtained with nearly saturated 4.3 mol kg −1 LiPF 6 /PC. The structure, viscosity, and ionic conductivity of the concentrated LiBF 4 /PC were investigated. Based on the experimental results, the rapid charge/discharge reactions at LiNi 0.5 Mn 1.5 O 4 electrodes were discussed.