Preparation Of Highly Dispersed Graphene Conductive Slurries And Application In Lithium Ion Batteries

Lithium ion battery is regarded as ones of the most promising energy storage technology due to its high energy density,energy conversion efficiency and output voltage.However,the anode and cathode materials of lithium ion batteries(e.g.,lithium iron phosphate,silicon monoxide and so on)generally have poor conductivity,which makes the electrode polarization in charging/discharging process,resulting in the capacity of material cannot utilize fully.To improve the conductivity of the electrode,zero-dimensional carbon black,one-dimensional carbon nanotubes and two-dimensional graphene are used as conductive agents for lithium-ion batteries.Graphene has attracted more and more attention due to its excellent electrical conductivity,high specific surface area and flexible two-dimensional planar structure.However,the few layers graphene is difficult to disperse evenly in solution due to its hydrophobicity and interlayer van der Waals forces.It is an important problem should be solved when the few layers graphene is used as a conductive agent.In this paper,graphene conductive slurries with high dispersibility were prepared by surface modification of dispersant combined with physical ball grinding and ultrasonic dispersion,and the effect on electrochemical performance of batteries was further investigated.Firstly,we explore the dispersion effect of dispersants polyvinylpyrrolidone(PVP),KD1 and BYK-2150 on graphene in the n-methylpyrrolidone(NMP)solvent.It was determined that the dispersant KD1 had the best dispersive and stable effect on the preparation of graphene slurries by means of ultraviolet spectroscopy and other characterization methods.The prepared KD1 dispersed graphene conductive slurry was applied to the lithium iron phosphate positive electrode(the graphene conductive agent accounted for 2% of the electrode mass)showed excellent electrochemical performance.The first discharge specific capacity is156.1 m Ah/g,and the retention rate of discharge capacity is high after 100 cycles of charging and discharging.The discharge capacity of the electrode under different current rate was measured,and the performance of the electrode was compared with the electrode with 10%acetylene black as conductive agent.Secondly,using deionized water as the solvent,the effects of dispersants polyvinylpyrrolidone(PVP),sodium carboxymethyl cellulose(CMC)and sodium lignosulfonate(SLS)on improving the dispersion stability of graphene were investigated.The experiment showed that the graphene after CMC treatment showed good dispersion stability,and the Si Ox negative lithium ion battery with the graphene conductive slurry showedexcellent electrochemical performance.The first charge(discharge)specific capacity was1273.8m Ah/g(1723.7m Ah/g)and showed a good cycling stability.The content of dispersant in graphene conductive slurry of graphene /Si Ox anode material was optimized,the stability of graphene conductive slurry of 1%CMC dispersants was observed,and the mechanism of its conductivity improvement was analyzed.Finally,graphene/carbon nanotubes composite conductive slurries were studied to build a better conductive network and further improve the electrochemical performance of the electrode.The influence of dispersant dosage on the dispersion state of CNTs in the electrode was first studied,and the composite conductive slurries were made with graphene slurries,and then mixed with SiO_x to prepare lithium ion battery cathode materials,and the electrode properties were tested.The process and composition of graphene/carbon nanotube composite conductive slurry were optimized.When the composite slurry was made from graphene slurry and CNTs slurry of 0.2%CMC,the first charging capacity of the electrode material was1176.3mah /g,with good cycling performance.In addition,the synergistic mechanism of CNTs and graphene in composite conductive slurry was discussed.