2. Experimental

2.1. Electrolyte and electrode preparation

Battery-grade ethylene carbonate (EC), propylene carbonate(PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC),diethyl carbonate (DEC), and lithium hexafluorophosphate (LiPF6)were purchased from Novolyte Technologies. Lithium foil (0.75 mmthick) was purchased from Alfa Aesar. All chemicals and materials were used as received. Electrolytes of 1.0 M LiPF6 in singlecarbonate solvents and carbonate mixtures (EC-EMC, EC-DEC, ECDMC, all in 3:7 volume ratio) were prepared in a vacuum glove box filled with purified argon.LiCr0.05Ni0.45Mn1.5O4 was synth

LiCr0.05Ni0.45Mn1.5O4 was synthesized by ball milling a mixture ofLi2CO3, NiO, Cr2O3 and MnCO3 (all from SigmaeAldrich) in stoichiometric amounts for 4 h by a heat treatment at 900 C for 24 h in air and a further annealing at 700C for 8 h. Details on the preparation and characterization of this material were reported elsewhere [23]. A slurry of LiCr0.05Ni0.45Mn1.5O4, Super Pconductive carbon black (SP, from Timcal), and polyvinylidene fluoride(PVDF, Kynar HSV900, from Arkema Inc.) in an N-methyl pyrrolidone(NMP, from Aldrich) solvent was prepared and cast onto an aluminum foil (from All Foils, Inc.). The weight ratio of LiCr0.05-Ni0.45Mn1.5O4:SP:PVDF was 8:1:1 and the active material loading was w4 mg cm2. After evaporating the NMP, the cathode sheet was pressed at 3000 psi for 1 min, die-cut into disks with a diameter of1.27 cm, dried at 110 C under vacuum overnight, and stored in the glove box. For comparison, an electrode sheet of SP-PVDF (1:1 by wt)was also prepared using the same procedures.

2.3. Electrochemical tests

The electrochemical oxidation stabilities of liquid electrolytes on different substrates were screened by linear sweep volt ammetry(LSV) in a beaker cell (inside the glove box) composed of three electrodes. Li metal was used as both reference and counter electrodes. The electrolyte samples on different working electrodes were scanned from the open circle voltage to 6.5 V vs. Li/Liþ at a scan rate of 0.1 mV s-1using a CHI 660C electrochemical workstation (CH Instruments). The cyclic voltammetry (CV) of the LiCr0.05Ni0.45Mn1.5O4 electrode in three electrolytes of conventional carbonate mixtures was tested on a CHI 1000A electrochemical station (CH Instruments) using Li metal as counter electrode. The samples were scanned between 3 V and different cutoff voltages from 4.9 to 5.3 V at a scan rate of 10 mV s-1. All the electrochemical tests were operated at room temperature.

Coin cell kits of CR2032 type were purchased from Xiamen TMAX Battery Equipments Limited. The negative covers, spacers and coin cell case were made of stainless steel 316 (SS-316), and the positive containers were Alclad SS-316. Whatman glass fiber B (GF/B) paper with a diameter of 1.91 cm was used as the separator since it has been reported to be stable at high voltages and has no wetting issues with electrolytes containing single cyclic carbonate solvents and EC-DMC mixture [15]. Li/LiCr0.05Ni0.45Mn1.5O4 half-cells with excess electrolyte were assembled on an electric coin cell crimper inside the glove box. The cells were cycled between 3.0 V and different cutoff voltages from 4.9 to 5.3 V at different current rateson Arbin BT-2000 Battery Tester.