New Energy Era
With the trend of global warming, major car companies have announced to withdraw from the era of fuel vehicles and enter the era of new energy vehicles.
Batteries are an important part of new energy vehicles.The current batteries mainly include ternary lithium batteries and lithium iron phosphate batteries.The maximum allowable mileage of new energy vehicles is related to the energy density of the battery, because the current lithium battery has low reversible specific capacity, poor rate performance, poor low temperature performance, short cycle life and poor safety performance，delocalized bonds and delocalized lattices of PI electrons endow graphene with good electrical conductivity, carrier and heat transfer properties.So graphene is considered as an ideal electrode material for lithium-ion batteries.
What is graphene ?
Graphene is a new single-layer, multi-layer two-dimensional honeycomb carbonaceous material exfoliated from graphite.Due to its unique structure, graphene has many excellent properties. The electron mobility of graphene (2x105cm2.v-1.s-1) is 100 times higher than that of silicon semiconductors.
Preparation of graphene
In order to compare the dispersing ability of graphene with different surfactant solutions, the dispersion degree of graphene with the same concentration of surfactant solutions (SDS/SDBS/PVA/SLS/CTAB/DNA/PVP) was investigated.
First, different surfactants were prepared into an aqueous solution of the same concentration, and an equal amount of graphene was added to it.In an ice-water bath, the power was 2000W ultrasonic for 2 hours. After ultrasonication, the dispersion was allowed to stand for 24 hours. The upper layer solution was centrifuged for 30min (rotation speed: 5000r/min), and then the upper layer solution of the centrifuge tube was taken to obtain a graphene dispersion with good dispersion.
The upper part of the centrifuge tube was extracted and diluted 5 times to test the absorbance. According to the Lambert-Beer law, higher absorbance corresponds to higher graphene dispersion concentration, and the solution obtained by using PVP as a dispersant has a higher absorbance value. Further test the ability of PVP solution to disperse graphene with different concentrations (0.1mg/mL, 0.4mg/mL, 1mg/mL and 10mg/mL).
The results show that the graphene dispersion with a PVP concentration of 10 mg/mL (graphene concentration of 1.3 mg/mL) can still maintain a uniform/stable state after standing for one month. The absorbance test (10 mg/mL of the dispersion was tested after 10-fold dilution) showed that the graphene concentration increased with the increase of the PVP solution concentration.
The results of thermogravimetric analysis show that the highest concentration of graphene that can be dispersed in 10 mg/mL PVP solution is 1.3 mg/mL. This is the highest value of graphene dispersion concentration obtained in the aqueous system using surface activity as a dispersant.
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