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.

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.

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The Mn-Cl co-doped LiFePO4 was succefully synthetized by two-step solid-state reaction. After doping, the Lattice constants shifted while the morphology changed only little, revealing that the properties may not be improved by the slight changed grain size but the crystal structure. The co-doped sample presented a high discharge capacity of 161.1mAhg−1 at 0.1C, 157.7mAhg−1 at 0.5C, 149.1mAhg−1 at 1C, nearly 30mAhg−1 higher than that of the pristine LiFePO4/C respectively. The electrochemical reversibility and cycle stability of co-doped LiFePO4/C were enhanced. Moreover, the Li+ diffusion and exchange current density of that was increased after doped with Mn2+ and Cl- .

Auto Regressive model (AR) of nanoTiN particles content in Ni-TiN composite coating was established by the method of Time Series Analysis. The trend of the nanoTiN particles content variation was forecasted with the AR model,and the prediction value and experimental test results were compared. The results show the model may forecast the nanoTiN particles content in Ni-TiN composite coating. And the average deviation is about 5.2884%. The average grain size for Ni and TiN is approximately 52.85 and 39.13 nm, respectively.