A Novel Technology On Preparation Of Batterty-Grade LiPF₆ By The Method Of The Complex Dissociation

Lithium ion batteries are the most prosperous energy storage batteries today.It's better than traditional batteries because of its good features of high energy density,high average output voltage,low self-discharge and no memory effect.In order to meet the requirements of lithium ion batteries' high voltage performance,its electrolyte need to have many characteristics,such as low molecular weight,easy to dissolve in organic solvents,stable electrochemical performance,etc.Lithium hexafluorophate(LiPF6)is white crystal and easy to reaction with moisture in the air.It has been one of the positive development of electrolyte in the current lithium ion battery industry because of better electrical conductivity and electrochemical stability.However its preparation is difficult because of the particularity of its chemical properties and high purity requirements.This paper has adopted the method of complex dissociation to prepare LiPF6 of battery level LiPF6 by pyridine?fluorophosphoric acid and lithium hydrate as the raw materials.First fluorophosphoric acid reacts with pyridine form intermediate C5H5NHPF6,and then this intermediate reacts with lithium hydrate made into LiC5H5NPF6,that last step is dissociating LiC5H5NPF6 into LiPF6 in homemade reaction vessel.Those products are characterized by XRD?IR?HNMR?AAS,and the electrochemical properties of LiPF6 is determined by assembling into the button batteries.The better technological conditions of preparing intermediate C5H5NHPF6 by neutralization reaction:the charge ratio of pyridine and fluorophosphoric acid is 1:0.8,reaction temperature is 30?,reaction time is 5h,Magnetic stirring speed is 600r/min.The product can be determined for C5H5NHPF6 by IR and HNMR,and the purity is higher.The optimum process conditions of preparing LiC5H5NPF6 by lithium exchange:the charge ratio of C5H5NHPF6 and lithium hydrate is 1:1,reaction temperature is 60 ?,reaction time is 5h,ethanol dosage is 10 ml,Magnetic stirring speed is 400r/min.The product can be determined for LiC5H5NPF6 by HNMR.It adopts the method of complex dissociation to prepare LiPF6 electrolyte in homemade reaction vessel and gets the optimum process condition:reaction pressure is 1Pa,reaction temperature is 30 ? reaction time is 8h.The product can be determined for LiPF6 with a purity of more than 99%by IR and HNMR.The results of testing the electrical conductivity of self-made LiPF6 in EC+DMC(50%DMC)mixed organic solvent is 11.42 ms·cm-1.The voltage platform of assembling button battery recharging is about 4V and discharge voltage platform is about 3.9 V.Stable charge and discharge voltage platform shows a better performance of lithium ion intercalation and deintercalation.The value of discharge specific capacity drops to 112.0 mAh/g from 134.4 mAh/g after looping 20 times under 1.0C rate,the capacity retention rate reaches 83.33%,the cycle efficiency reminds at around 91.38%.