2032-type cells were built with Elexcel cathode (d=14.7 mm) comprising a composite of 92 wt.-% LiNi_0.5Mn_1.5O₄, 4 wt.-% conductive carbon and 4 wt.-% polyvinyliden fluoride and Elexcel graphite anode (d=15.0 mm), a trilayer polypropylene/polyethylene (PP/PE/PP) separator (d=19 mm, Celgard), and one layer of glass fiber separator (d=16 mm, thickness=0.67 mm, Whatman) and 100 microL of electrolyte in each cell in an Argon-filled glove box in which the water content is smaller than 0.1 ppm. Cells were cycled on an Arbin cycler and the temperature was controlled by Fisher Scientific Isotemp Incubators.

3. Cycling performance

LiNi_0.5Mn_1.5O₄/graphite cells were cycled at 25° C. initially with the following cycling protocol: C/20 for the first cycle; C/10 for the second and third cycle; and then C/5 for the remaining at 25° C. After 25° C. cycling, cells were transferred to 45° C. to perform C/5 cycling for 50 cycles. Cells were charged with a CC-CV mode, constant current charge to 4.25 to 4.8 V and followed by a constant voltage charge step 4.8 V vs. LiC₆/C₆ until the current decreased to 10% of the applied charging current. Then, cells were discharged to 3.30 V vs. LiC₆/C₆ at same constant current (CC mode).

The results of the cycling tests with base line electrolyte (comparative), baseline electrolyte containing 0.5 wt.-% pyridine-SO₃ complex (comparative) and baseline electrolyte containing 0.5 wt.-% 2-vinyl pyridine-SO₃ complex (inventive) are shown in FIGS. 1a) and 1b).

The efficiency is calculated by equation: Efficiency=(Discharge capacity of n^th cycle/Charge capacity of n^th cycle)*100%.