Investigation Of High And Low Temperature Electrolyte For Lithium-ion Battery

As a new generation of chemical power system,lithium-ion batteries have many advantages such as high energy density,long life and reproducible et al. It will gradually replace the traditional nickel-metal hydride,nickel cadmium and lead-acid batteries and becomes the most popular secondary battery. After 20 years' development,lithium-ion batteries have been widely used as power source of cell phones,digital cameras,laptops and so on, and has become the mainstream power of new energy vehicles in recent years. Although the lithium-ion battery has many advantages,there are some problems when lithium ion battery as a power source at present. For example,the battery is much shorter for the requirements of electric vehicles?10 to 15 years?;the battery will cause safety problems such as explosion under abused conditions;and the battery decays quickly at elevated or reduced temperatures??60 °C or ?-20 °C?. These problems are closely associated with the performance of the electrolyte. This paper aim at resolving the stability and safety of the lithium-ion battery around the the components of electrolyte?organic solvent, lithium salt and additives?.?1?New solvent methyl acetate?MA? and acrylic acid methyl ester?MP? as an organic solvent were applied to the electrolyte used in lithium-ion batteries. Adding a certain amount of MA or MP can effectively reduce the viscosity of electrolyte and improve electrolyte conductivity at low temperature,especially significantly improve the low temperature performance of lithium-ion batteries.?2?On the basis of optimization of the solvent, adding fluorine generation ethylene carbonate?FEC? as the electrolyte additives. It is found that FEC was electrochemical reduced on graphite prior to electrolyte solvents,participating in SEI film formation and exhibit higher rate performance and discharge capacity at low temperature of the Li/Graphite half-cells. Simultaneously, the formation of inorganic components, such as Li F and Li_xPO_yF_z, on cathode surface was suppressed,and this results improve the conductivity of interface film on cathode, speeds up the mobile rate of Li+ in the electrolytes.?3?We obtained a electrolyte with excellent electrochemical performance at a wide temperature range by using difluoro?oxalate?borate?Li ODFB? as Li salt, g-butyrolactone?BL?and ethyl methyl carbonate?EMC?as main solvents. This salt dissolved in solvents is superior to ionic conductivity than LiPF₆-based electrolyte in the range of-20-80 °C, moreover LiODFB-based electrolytes systems significantly improved its thermal stability. The integrity of LiCo_1/3Ni_1/3Mn_1/3O₂ electrode surface cycled after high temperature is much higher than LiPF₆-based electrolytes.?4?Lithium-ion batteries showed high capacity retention and cycle stability at a wide temperature range adding additive LiODFB in LiPF₆-based electrolyte systems. LiODFB formed a good solid electrolyte interface film?SEI? in LiCo_1/3Ni_1/3Mn_1/3O₂ electrode and Graphite electrode by X-ray photoelectron spectroscopy?XPS? test, which contains fewer inorganic substances, such as LiF and Li_xPO_yF_z, increasing the ionic conductivity of the electrolytes.