Lithium battery conductivity

　　Conductivity is an important parameter for measuring the performance of electrolytes, which determines the internal resistance and rate characteristics of electrodes. High conductivity is a necessary condition for achieving good low-temperature performance of lithium-ion batteries. From the perspective of organic solvents, the main factors affecting conductivity are the dielectric constant and viscosity of the solvent. The larger the dielectric constant of the solvent, the weaker the electrostatic force between lithium ions and anions, making it easier for lithium salts to dissociate and increasing the number of free ions. The viscosity of solvents mainly affects the migration rate of free ions. The higher the viscosity, the lower the migration rate and conductivity; On the contrary, the opposite is true. Therefore, it is required that the solvent has a high dielectric constant, low viscosity, an appropriate liquid temperature range (low melting point, high boiling point), and a high solubility of lithium salts in it to ensure sufficient high conductivity. Cyclic carbonate EC has a high dielectric constant and boiling point, but its viscosity and melting point are also high; Linear carbonates I~(DMC, DEC, EMC) have lower viscosity and melting point, but lower dielectric constant and boiling point. Based on the advantages and disadvantages of a single solvent component, actual organic electrolytes often use binary and multicomponent mixed solvents composed of EC and other solvents. By optimizing the ratio of solvent components and relative amounts, reducing the content of high melting point component EC and increasing the content of low viscosity and low melting point components (known as low-temperature co solvents), the low-temperature conductivity of the electrolyte can be effectively improved, thereby achieving the goal of improving the low-temperature performance of lithium-ion batteries. Like Smart? The electrolyte system reported by others at 1.0mol/LLIPFdfEC: DEC: DMC: EMC) f1:1:1:3 (volume ratio) can achieve an ion conductivity of 1.32mS at~40 ℃? Cm~l: The battery can achieve 80% of its rated capacity and stable cycling performance after cycling at -20 ℃ (charging at 1/10C and discharging at 1/5C)- A rated capacity of 70 can be obtained by cycling at 40 ℃ (charging at 1/15C and discharging at 1/10C). L_F.Xiaol。 The electrolyte system J.0mol/LLIPfEC: DMC: EMC reported by others (1:3:8, mass ratio 1, -40. C) achieved a room temperature capacity of 90 at 1/10C discharge. Except for linear carbonates, linear alkyl esters have a lower melting point, which is 20-30 ℃ lower than commonly used carbonates. They are usually studied as low-temperature co solvents for electrolytes. For example, methyl formate (MF, melting point -99 ℃) l3l, methyl acetate (MA, melting point -98 ℃) _4_, ethyl acetate (EA, melting point -83 ℃) E4,51, ethyl propionate (EP, melting point -73 ℃) [41, methyl butyrate (MB, melting point -84. C) [51, and ethyl butyrate (EB, melting point -93. C) 4l can all improve the low-temperature performance of lithium-ion batteries to a certain extent.

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