10.1016/j.mee.2015.01.022
Performance improvement of lithium ion batteries using magnetite-graphene nanocomposite anode materials synthesized by a microwave-assisted method

Graphene oxide (GO) was prepared from graphite powder by the Staudenmaier method [24]. First, sulfuric acid and nitric acid were mixed well by stirring 15 min in an ice bath, and then graphite powder was dispersed into the solution. After 15 min, potassium chlorate was added into the system - very slowly to prevent strong reaction during the oxidation process. After reacting for 96 h, the mixture was diluted by de-ionized (DI) water and then filtered. The GO was next washed by hydrochloric acid to remove sulfate ions from the solution, which could be detected by adding BaCl2 in solution. After that, the mixture was repeatedly rinsed with DI water until its pH value became neutral. Finally, before the GO was ground into a powder in an agate mortar, the GO solution was filtered and dried in an oven at 80 degC overnight. 

The GO powder was dispersed in DI water (1.5 mg/ml) by ultrasonication. The solution was mixed with Fe(NO3)3, urea, and ethylene glycol (EG) to form a homogeneous suspension. Next, the mixture was heated with different microwave powers - 200, 600, and 1000 W - under a reflux condition for 30 min. Before being dried overnight in the oven, the products were purified by washing repeatedly with DI water. Finally, Fe3O4/graphene nanocomposites were obtained by thermal reduction in an Ar atmosphere at 873 K for 4 h.

sulfuric acid and nitric acid
mixed
15 min
min
potassium chlorate
added
15 min
min
mixture
reacting
96 h
h
GO solution
dried
80 degC
degC
DI water
1.5 mg/ml
mg/ml
microwave powers
200, 600, and 1000 W
W
microwave powers
600, and 1000 W
W
microwave powers
1000 W
W
mixture
reflux condition
30 min
min
thermal reduction
873 K
K