In order to overcome the limitation of Li-ion batteries at low temperature, series of electrolytes are prepared. Specially，FEC is chose to work as electrolyte solvent to enhance its poor performance. Electrolytes are composed of EC, PC, EMC and FEC, while VC is added as additive. Electrolytes with different ratio are examined, then the electrolyte with the best conductivity is studied in detail. Its characters are evaluated by CV, EIS and charge/discharge tests et al. The discharge curves of LiCo1/3Ni1/3Mn1/3O2/Li show that battery with this FEC-based electrolyte at 233K could yield 51% of room temperature capacity. Most obviously, MCMB/Li half cell with this electrolyte could fill 91% of its normal capacity at 233K while batteries barely charge any with traditional electrolyte（LiPF6/EC+DMC(1:1 in volume)）. This nice charge behavior won’t emerge unless the conductivity could basically meet the demand at 233K. The property of FEC-based electrolyte outweighs commercialized electrolyte as this article confirms.

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A new type of electrolytes for low temperature operation of Li-ion batteries was formulated in this work. Instead of LiPF6, LiBF4 and LiODFB were used to form this new type of electrolytes, although LiPF6 is the mostly chosen solute in the state-of-the-art Li-ion electrolytes. It was found although a LiBF4-based electrolyte had a lower ionic conductivity than that of a LiODFB-based electrolyte, a LiODFB-based electrolyte demonstrated improved low temperature performance. In particular, at-30°C, a Li-ion cell with 1M LiODFB dissolved in a 1:2:5 (wt.) propylene carbonate (PC)/ethylene carbonate (EC)/ethyl methyl carbonate (EMC) mixed solvent delivered 86% of the capacity obtained at 20°C. Furthermore, the cells with a LiODFB-based electrolyte showed lower polarization at-30°C. The above results suggest that beside the ionic conductivity of an electrolyte as a limitation to the low temperature operation of Li-ion batteries, there was interface impedance having effect on it. Analysis of cell impedance revealed that reduced charge-transfer resistance by using LiODFB resulted in improved low temperature performance of Li-ion batteries.

Sulfurized polyacrylonitrile was well known for its excellent electrochemical performance. In this work, a kind of gel polymer electrolyte with PMMA as polymer matrix was prepared through in situ thermal initiated polymerization in this work. The interactions between polymer and traditional carbonate electrolyte were studied by IR. Its electrochemical performance in Li/SPAN batteries was investigated in detail, using LSV, CV, EIS et al. The results show that high ionic conductivity was achieved, with a value of 4.2 mS cm-1 at 30◦C when the content of PMMA was 15%. A reversible capacity of 975.3 mAh g-1 could be maintained after 50 cycles.

AlF3 and MgF2 were applied to modify the surface of the LiNi1/3Co1/3Mn1/3O2 cathode material. The structural and electrochemical properties of the materials were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), charge–discharge tests and electrochemical impedance spectra (EIS). The results show that the 1 wt.% AlF3 and 1 wt.% MgF2 coated LiNi1/3Co1/3Mn1/3O2 (NCM333) cathode material exhibits an optimized electrochemical performance. It presents an initial capacity of 207.2mAh/g and 169.1mAh/g at 0.2C between 2.8V and 4.7V after charge-discharge 65 cycles. The rate performance is also enhanced because the coating decreases the interface charge transfer impedance.