Low‐Viscosity γ‐Butyrolactone‐Based Concentrated Electrolyte Solutions for LiNi0.5Mn1.5O₄ Positive Electrodes in Lithium‐Ion Batteries

Highly concentrated electrolyte solution with a low viscosity and high stability against oxidation was obtained by using a single solvent system of LiBF 4 /γ‐butyrolactone (GBL). Although up to 4.65 mol kg −1 LiBF 4 could be dissolved in GBL at room temperature, 3.87 mol kg −1 LiBF 4 /GBL was a reasonable compromise to attain a low viscosity (52.1 mPa s) and a low GBL/Li molar ratio (3.00). Sodium carboxymethylcellulose and poly(acrylic acid) were used as binders for the spinel LiNi 0.5 Mn 1.5 O 4 positive electrode and the graphite negative electrode, respectively, to suppress the swelling of conventional poly(vinylidene fluoride)‐based binder. The charge and discharge performances of the LiNi 0.5 Mn 1.5 O 4 positive electrode and the graphite negative electrode were improved by using 3.87 mol kg −1 LiBF 4 /GBL, as compared with concentrated propylene carbonate‐based electrolyte solution.